A nun broke a young girl's arm as she reacted to discovering the child was being sexually abused by a priest, an inquiry has heard.

A witness told how she had hoped she would be protected when the nun walked in on the assault in 1970, when she was eight, but was instead called a "whore", grabbed and thrown towards a wall.

Theresa Tolmie-McGrane said she was then given a "real hiding" by another nun and threatened with having her other arm broken if she told anybody what had happened.

Ms Tolmie-McGrane waived her right to anonymity at the Scottish child abuse inquiry to recount a catalogue of other abuses during her 11 years at Smyllum Park orphanage in Lanark, South Lanarkshire, which closed in the 1980s.

These included beatings, humiliations, freezing showers and children being force-fed inedible food, being told to eat their vomit and having their mouths rinsed out with soap.

The witness told the hearing in Edinburgh how she arrived at the institution, run by the Daughters of Charity of St Vincent de Paul, at the age of six in 1968 after an abusive early childhood.

She recounted how, about two years later, she had a job dusting pews in the church.

One particular priest would arrive early and ask her to sit on his lap, before progressing to making her to perform a sex act on him or watch as he did so, the inquiry heard.

"He said 'I need you to be a soldier of God, a good little soldier'," she told the inquiry, adding the abuse went on for several months.

On one occasion, a nun walked in to the room as it was happening, she said.

She told the hearing: "I thought 'praise the Lord, she's seeing this, she's going to be angry with him and protect me'.

"Her whole face became distorted. I thought 'she's angry with him', (but) she was angry with me.

"She called me a whore, she took my left arm and yanked me out of his lap and flung me across to the wall (and said) ... 'get the f*** out of here'."

She told how she crawled away and had to go back to church, but when another nun found out she could not raise her arm she was given "a real hiding".

"I said I couldn't lift my arm, my arm hurt. I said (a nun) has broken my arm," Ms Tolmie-McGrane said.

She told the inquiry how the second nun took her to hospital but warned her: "Don't you dare tell anybody what happened, young lady, or I'll break your other arm" and assured her she would be "lying to protect a man of God, so it's ok to lie".

Ms Tolmie-McGrane, who later went to Glasgow University and now works in Norway as a psychologist, told the inquiry she was at Smyllum from 1968 until 1979.

She described how, on her first night there, she was slapped after waking up screaming from a nightmare, then forced into a freezing cold shower for wetting the bed.

If a child vomited, they would have their faces rubbed in it or be told to eat it, she said.

The witness also described beatings at the hands of nuns, sometimes with the crosses they wore.

"I would say every child at some point would have been hit with a cross," she said.

Children would be made to sleep in soiled sheets for two or three nights as a punishment for bed-wetting, she said, and when they went on an annual holiday to Ayrshire, they would end up badly burnt and blistered from the sun.

The inquiry also heard how one girl would run away often but never returned after being run over by a car one day.

Ms Tolmie-McGrane told the inquiry she approached police officers visiting Smyllum on two occasions to tell them "the nuns are hurting me" but was "marched back in" to the institution on both occasions and then beaten by a nun.

Injuries from her time at Smyllum included a facial scar and broken tooth from being "slammed into a wall", broken fingers from being hit with a hair brush and a broken tail bone from having a seat pulled out from underneath her when she was sitting down.

"I have, unfortunately, physical scars, not just emotional ones," she told the hearing.

Ms Tolmie-McGrane recounted an occasion when, aged 13, she ran away from a nun who "was always trying to touch me" and squeezed her breasts.

She said she spoke about the instances of sexual abuse during confession with different priests.

"The answer I got was 'pray for them'," she said.

She recounted how Smyllum staff would lock her in a dark pantry as a punishment, knowing she had a fear of the dark.

Another punishment involved children having their mouths washed out with carbolic soap, she said.

Residents would also be separated from their friends, she told the hearing, saying: "We just thought they didn't want us speaking about what was going on."

Ms Tolmie-McGrane, who achieved five A grades in her Higher exams, also told how she would have to do her revision in the toilets after bedtime and would be called names by the nuns when she did well in her education.

Asked what lessons should be learned, she told the inquiry: "I think it's important the Catholic Church figures out who the bad nuns and priests are and has them removed."

She added: "The child should always be believed."

Colin MacAuley QC, counsel to the inquiry, put it to her that a particular nun has been spoken to by the inquiry and does not accept the allegations.

The witness replied: "All I can say is I have no reason to lie, but she maybe has a lot to lose."

The inquiry, chaired by Lady Smith, continues.