Sophie Donaldson is Liz Birdsworth's daughter. Sophie got arrested for vehicular manslaughter and ended up in Wentworth where her mother was. She had been charged for drunk driving before and that's why she didn't get bail. Lucy Gambaro and some of her mates try to rape her, but Franky Doyle stops them with a broomstick. Liz doesn't like that Franky and Sophie are hanging out. She goes to apologize to Liz but finds her drunk in her cell and tells Franky, then a fight starts between Liz and Franky which ends up getting Doreen Anderson hurt.
In the episode 3x10, Sophie is found naked in Franky’s cell, willing to make her a surprise as the peak of her extremely intense and developing esteem and trust towards her since she entered the prison. Franky, by the way, will refuse to have sex with Soph, being busy preparing her parole hearing.
In the end of the season, tensions between Donaldson and her mother will fade away after a deep interior change due to desperation.
Liz will help and accompany her daughter to one of the most touching moments in her life in prison: the face-to face meeting with the wife of her car accident victim. In the final scene of episode 3x12, the two of them are shown standing side to side in the courtyard.
In the episode 4x01 it is mentioned that she was transferred to Barnhurst.