A nun fighting Katy Perry's purchase of a former convent is fired up and reaching out to a higher authority -- Pope Francis himself -- to intervene in the case that has brought the “Roar” singer a rash of negative publicity.

“They’ll have to kill me first if they want to keep me quiet,” Sister Rita Callanan, 80, told Fox News this week, referring to the Roman Catholic Archdiocese of Los Angeles, which she said wrongly sold the property to Perry. “I am asking Pope Francis to intercede."

Callanan and her attorneys hope the pontiff will review the case and speak to the Signatora, the highest court in Rome. "It’s like the U.S. Supreme Court,” according to Callanan.

The nun says the death last month of Sister Catherine Rose Holzman - a close friend and ally in the fight over the sale of their order’s convent on eight acres in the Los Feliz area - has motivated her to stay in the battle, despite urgings by doctors and friends to drop the matter for health reasons.

NUN IN KATY PERRY LAWSUIT DIES AFTER COURTROOM COLLAPSE

They'll have to kill me first if they want to keep me quiet. I'm asking Pope Francis to intercede. — Sister Rita Callanan, who is in a court fight to keep an old convent from being sold to Katy Perry

Callanan and Holzman, who was 89, vowed they would fight to the end for the property the Sisters of the Most Holy and Immaculate Heart of the Blessed Virgin Mary owned for more than 40 years. That ended when, as the nuns tell it, the Archdiocese of Los Angeles forced them out.

Callanan said she, Holzman and other nuns who lived at the property had seen it as their "Motherhouse," where they would grow old together, and look after one another.

The letter to Pope Francis, in which Callanan also appeals for a meeting with the pontiff, says the nuns "were promised that we would always be taken care of by the archdiocese and that we would live out the rest of our lives at our convent. After we are all gone, the Archbishop would inherit our property … Archbishop Gomez has broken these promises to us."

"He tried to sell our convent without our approval to a person whom we do not support. It is the pop star Katy Perry," the letter reads. "We do not agree with her lifestyle that has strayed far from any faith … At the end of our lives, we find ourselves fighting for justice and for what is right."

The archdiocese sold the property to Perry for $14.5 million, but the Vatican must give its approval before the deal is considered final.

Archdiocese officials deny they broke any agreement with the nuns, and say they have acted with their best interests in mind.

"The main concern of the Archdiocese of Los Angeles is and has always been the care and well-being of all the ... sisters," Adrian M. Alarcon, director of media relations for the archdiocese, told Fox News on Wednesday. Alarcon said the property has been vacant since 2011 "because it became too costly for the five remaining sisters to maintain and no longer accommodated their physical needs."

Holzman died on March 9 after collapsing in a courtroom for a hearing related to the case. She signed the letter to the pope before she died.

The two nuns had wanted a friend and entrepreneur, Dana Hollister, to buy the property instead of Perry, trusting that Hollister would honor the spirit of their former homestead. But a judge last year voided the sale to Hollister and ruled the archdiocese, and not the nuns, had the right to sell the property.

“Two days before she had this heart attack she called me and said ‘You know, Rita, this stress the archbishop is putting Dana through is just killing me,’” Callanan recalled. “In court she was in front me and during recess she said ‘My chest hurts,’ and she collapsed on my lap, right on my lap.”

The main concern of the Archdiocese of Los Angeles is and has always been the care and well-being of all the [Immaculate Heart] sisters. — Archdiocese of Los Angeles

“I can’t believe we’ve been treated the way we have,” Callanan said, adding the archdiocese conducted the negotiations with Perry without informing the nuns, who learned of the deal through a third party. “Here were two elderly sisters who should be living peacefully after serving the Lord for many years and we’re put through this.”

Holzman expressed her anguish in an interview with a local Fox affiliate station just hours before she died. Holzman said: “Katy Perry, please stop. It’s not doing anyone any good [and it’s] hurting a lot of people.”

Perry's pulblicist declined to comment for this story. Published reports have said Perry wants to live on the property with her mother and grandmother.

Meanwhile, archdiocese officials have said the remaining nuns from the order will be taken care of. Callanan said that's not the case, adding that she often finds herself struggling.

“We were in this archdiocese for so many years, and then to be thrown under the bus,” she said. “These things are inexcusable."

Callanan said isn't going to shrink from the fight, not even if it means going up against the popular "American Idol" judge and the archdiocese.

“It’s very much, to me, a David and Goliath fight,” the nun said. “And you know who won that battle.”