A 58-year-old woman who has tried for over 40 years to find her sister gave evidence to Northern Ireland's Historical Abuse Inquiry.
The woman, who now lives in the Republic, spent 12 years in Derry's Nazareth Home from 1957 until 1969.
She did not know she had a sibling in the home until one day when she was on a foster placement with another of the residents, who said to her "I'm your big sister".
Giving evidence to the inquiry in Banbridge, she said her sister left the orphanage as a 16-year-old and that she tried to take her with her but that she was too young to go.
The woman, named Joan, told the inquiry: "I've been trying to search for my sister for a long time since I left the convent, but I just can't find her."
She told how she discovered, three years ago, that she had three other siblings, a brother and two sisters, who had been raised by their grandparents.
Her description of life in the Nazareth Home in Derry's Bishop Street included an allegation of being lined up for baths with 100 other young girls and the same water being used to wash them.
Joan also made claims of beatings she regularly received from some of the nuns. She said that some of the nuns were kind but others were cruel.
She said: "I could have done better ... they ruined my life. I want an apology ... I would never want anyone going through what I went through. I could have done better. They ruined my life."
Joan was the first former resident of the girls' home in Derry to give evidence to the inquiry, which was set up by Northern Ireland's power-sharing administration.
It is investigating what took place in 13 residential homes, which were run by the Catholic Church, voluntary organisations and the state between 1972 and 1995.
It is expected to complete its work at the end of next year and to produce a report in 2016.