What options were there, for Sara?
Placed with her father, who had a history of abusing women and neglecting children;
Placed with her mother, who had a record for biting a child, possibly learning difficulties, and a history of violence and neglect of children;
Long term fostering, which as Twiglets says, has poor outcomes for children on any metric;
Adoption and the chance to grow up with a vetted new family.
That's it, that's all the options that existed for Sara and she was completely failed by those who had power over her life. You seem determined to believe that she'd have gave been better off with her mother but while she'd be better off as in not dead, that a very low bar indeed isn't it? Neither of her parents 'care' was good enough. Being alive is better than being dead but she'd still have had an awful abusive childhood. It's not good enough.