@Paulmolark
Is she able to act abusively to any other children? I note that point was picked up on by one therapist you mentioned. If so have you considered involving the authorities for what sounds like historic child abuse.
Reminds me of the "lovely" JW Eunice Spry in England who's adult foster children finally took her to the authorities and she served 6 years in the slammer. Due out this month in fact.