Sister Rita Callanan has been at the centre of a legal dispute involving pop star Katy Perry

Struggling with ill-health, including breast cancer, Sister Rita Callanan looks into her pantry for scraps of food and sees, yet again, only cereal.

Her bank balance is zero, her healthcare cheque has bounced on more than one occasion and she's not sure who's going to foot the bill for her next round of cancer treatment.

Now 80 years old, she scratches her head in bemusement as to how this has all happened. A few years ago, she had hundreds of thousands in the bank and was a paper millionaire.

As one of the few remaining sisters alive, who belong to the historic Order of the Immaculate Heart of the Blessed Virgin Mary in Los Angeles, her future was secure. Their historic convent sits in the uber trendy Los Angeles suburb of Los Feliz and is today worth in excess of £10 million.

That is until Katy Perry came along. The 32-year-old singer tried to buy it without the nuns' permission. She agreed a deal with the Royal Catholic Archbishop of Los Angeles (RCA), headed by Archbishop Jose Gomez, who claims the convent is under its ownership and sold it to Perry for £10 million in July 2015.

Katy Perry wants to purchase an historic convent in Los Angeles worth £10m (pictured), which is owned by historic Order of the Immaculate Heart of the Blessed Virgin Mary

The convent (pictured) sits in the uber trendy Los Angeles suburb of Los Feliz and is today worth in excess of £10 million. The order of nuns say they have owned it for 45 years

Pop star Perry agreed a deal in 2015 to buy the convent with the Royal Catholic Archbishop of LA, headed by Archbishop Jose Gomez, who claims the convent is under its ownership

But Sister Callanan (pictured) and her fellow Sister Catherine Rose Holzman, 89, had claimed that it's been the Order's property for 45 years and it's their right to sell it and nobody else's

Pop singer Katy Perry agreed a deal in 2015 with the archbishop to buy the convent for £10m

But two nuns took exception to this. Sister Callanan and her fellow Sister Catherine Rose Holzman, 89 - a combined age of 169 years - claimed that it's been the Order's property for 45 years and it's their right to sell it. They found a buyer in property developer Dana Hollister.

On Friday, in the latest round of the epic court battle, Sister Holzmann tragically collapsed and died in the Los Angeles courtroom. Now only Sister Callanan remains in the fight against Perry and the RCA. Sister Callanan has vowed to keep on fighting and asked the public to help the cause, setting up a GoFundMe page to help with their legal costs.

She says: 'On March 9th, 2018 we tragically lost Sister Catherine Rose, my beloved fellow IHM Sister and original organizer of this GoFundMe campaign. She was my cherished partner in this ongoing legal battle to keep our convent. It is now more important than ever to continue this fight and for our cause to prevail.'

Independent of who is right or wrong, amid such a complex legal battle, there's the human cost. Sister Callanan is suffering from cancer and diabetes while multi-millionaire Perry told the nuns that she wants the stunning 22,000ft Mediterranean-inspired property so that she can 'sip green tea and find herself'.

Our exclusive images show why the stunning property - which was designed in an Italianate and Mediterranean style and has a monastery, fountains, a pool, and stunning views over the San Gabriel Mountains - is at the heart of such a fierce battle.

The house was built in 1927 for broadcaster and entrepreneur Earle Anthony, who enlisted the help of architect Bernard Maybeck. After being purchased by Sir Daniel Donohue and his wife Countess Bernardine Murphy Donohue in the early 1950s, they virtually gave it away to the sisters, who pooled their money together, and paid £431,000 in 1972 and paid it off over three years.

Sister Callanan says: 'All we are asking is to sell our own property, keep our own money so we can take care of ourselves until the last person dies, then the money and property can go to the archbishop. There's not many more years, give me a break. He's supposed to be a chief shepherd.

In 2005, Archbishop was supposedly given the go-ahead by the Vatican to take control of the convent although this point is now being disputed. A 'pontifical commissary' was put in place - like a conservator of the estate - who assumes responsibility for the sisters.

But Sister Callanan says: 'He claimed that Rome gave him permission, now we did a lot of research and Rome has done research, and these claims, this letter to give him authority was not from Rome, but a friend of the archbishop's.

According to Sister Callanan, he started 'sending us to retirement homes, one by one, separately, so we weren't a unit.' She says all their bank accounts were closed - they each had upwards of £215,000 in their accounts.

'All these years of my religious life, I would never have expected to be fighting an archbishop to keep our own property and money, so we can care for ourselves. We don't want the archbishop handling our money.

Sister Callanan is now at a tiny convent attached to St Bernadette's Catholic Church in Los Angeles; the convent is a depressing building, grey and cold, not even a hundredth of the size of their spiritual home.

The house at the centre of the dispute was built in 1927 for broadcaster and entrepreneur Earle Anthony, who enlisted the help of architect Bernard Maybeck

The sprawling convent was purchased by Sir Daniel Donohue and his wife Countess Bernardine Murphy Donohue in the early 1950s where they lived there until the early 1970s

The Donohues virtually gave the property (pictured) away to the sisters, who pooled their money together, and paid £431,000 in 1972 and paid it off over three years

Katy Perry has been embroiled in a legal battle with the Sisters of the Immaculate Heart of Mary since early 2015 over their former convent

She lives frugally and can't buy expensive groceries, as she now has to rely on a stipend - a regular sum of expenses - from the RCA, which she says is barely enough to survive and was reduced this month. She says the archdiocese refuses to pay any of their legal bills.

'The archdiocese pays my rent and bills where I am - £358 for rent and £179 for a housekeeper - but the rest comes out of my stipend, which they've reduced by £538 a month,' she explains.

'My health insurance has only been partly paid recently - I got cancellation notice from health insurance, as they didn't pay the bill, so I had to borrow money from a friend as I didn't want it cancelled. I was two months in arrears. They better pay it back to me.

'I have health issues, I have diabetes and breast cancer. They don't pay some of the bills on time, I said when it comes to this sort of insurance, you have to pay it. I don't know if I'm covered, I'm supposed to be, that's all I know. Sister Catherine Rose had an unpaid medicine bill for £500 then she made out a check to the pharmacy and it bounced. It's horrible.

'He is claiming he's taking care of us, that's not true. We send bills up there and they don't get paid. I get my stipend, but it's not leaving my enough for living expenses for the way the cost of living has risen groceries.

'I pay automobile costs, supermarket fees, magazine subscriptions, and also running a house isn't cheap. I've got family members who are very sick, close family members have died including my own sister, there's so many things, it's just punishment.

Sister Rose Catherine Holzman, 86, (left) and Sister Rita Callanan, 78, (right) were locked in a battle over who has the right to sell the historic convent where they once lived. Sister Holzman collapsed and died in court last Friday after telling the star to back off leaving Sister Callanan

The Sisters said they had found a buyer in Dana Hollister. Hollister filed for bankruptcy and list's Perry's company - The Bird's Nest, LLC, as one of her creditors to whom she owes £3.73m

Sister Callanan says that she found out about the sale of the convent to Perry by the archbishop though a friend, and claims the archbishop did this without consulting the sisters

'I was yelling and reporting it to Rome, they have now sent a check so I have money for groceries. Everything they don't pay for us, it goes right to the Pope. The Vatican is well aware of what this man is doing.

'It's caused us so much duress. I had to go for a chest X-ray as I thought I had pneumonia. I wanted to turn my back, but I couldn't. I've been the one leading the charge, I couldn't leave this. Does it affect my health? Yes, it does. My doctor knows what this man [the archbishop] is doing, she's a Catholic, but she's not practicing because of this man. I ask God: 'What's going on?' 'Course it makes you question your faith. But I've got to believe. I have to say: 'Lord increase my faith.'

Sister Callanan says that she found out about the Perry sale though a realtor friend, and claims the archbishop did this without consulting the sisters.

'I had a real estate package a friend had given me, showing that this archbishop had everything settled to sell to Katy Perry. I told him that I know she has a license to be able to throw parties until 1am, have x amount of people over, he tried to tell me it was just 'exploratory', I said: 'This is not exploratory, I am not stupid.' They call it machismo,' says the sister.

In the archdiocese's defense, it states that the main concern 'is and has always been the care and well-being of all the IHM Sisters.' Three of the five sisters who are alive have sided with the archdiocese although Sister Callanan says this is because they're all older than her and blindly believe 'whatever the archbishop tells them,' before adding: 'One of the sisters is on morphine twice a day, you're telling me she can make decisions? No, she cannot. I'm also the youngest at 79.'

Ultimately, Sister Callanan says she will have to accept the decision, whichever way it turns out, although other nuns in the US are looking on at this unique case. She thinks this is a test case which means that, if they lose, any archdiocese could stake a claim for ownership of convents in its area.

'It's been a horrible fight for women who have been in religious life for so long who have done so much for our archdiocese. It was our property, we had the deed, he said he had the authority and had a letter from Rome from his friend that wasn't even recorded. It was a lie,' she says.

'We just want to sell our own property. We live a very simple life. Catherine Rose, is in St John of God Gard Retirement Home in LA, the others are at Nazareth House [an assisted living convent].

'If he can take our money, so can any archbishop or cardinal anywhere, the other sisters are watching us. Instead of standing up with us and fighting, they're hiding their money, pretending they haven't got any, as they don't want this to happen to them.

'They say watch your back, but you go on and live your life.'