The witness also said her family had been forced to move to Spain to escape her daughter's alleged abusers.
Sheffield Crown Court also heard how police lost tapes of an interview with defendant Sageer Hussain in 2003.
Eight men, including Mr Hussain, deny sexually abusing three girls between 1999 and 2003.
The mother of one of the alleged victims said in a statement: "Her character changed from a lovely girl to an animal. She became horrible."
She said at one stage she discovered a mobile phone in her daughter's bedroom and rang a number stored under the name 'Waleed'.
She said a man picked up the phone and said "I ain't done owt, I ain't touched her. It isn't me".
When she asked her daughter about the phone she said she burst into tears and said "They're raping me, they're raping me".
She told the court after her daughter went to the police in 2003 her family were repeatedly threatened.
"We were so distraught that we sold the business and the home and moved to Spain," she said.
Det Con Andy Stephanek, of South Yorkshire Police, told the court the force had lost the tape of an interview with Mr Hussain when he was first questioned about the allegations.
He said it appeared that "due to the passage of time they've been destroyed".
The trial continues.
A woman who was allegedly raped and abused by eight men in Rotherham changed from a "lovely girl to an animal", her mother told jurors.