Marriage and revoking power of attorney?

My Step father is termially ill in hospital and can no longer walk. His daughter has manged to get him to give her POA. She opened an account in his name and removed £12K from his joint account with his wife (my mother) I believe his daughter has engineered this. Is this legal, has my mother any rights to recover the money. He has done this as he has been convinced my mother will not be able to look after him once he is released They were happily married before he went hositpal. My Mother scared and confused. The house Alli Online is owned outright and in joint names, can they force her to sell the house? His daughter has a very bad credit rating and I think she is taking for the money for herself knowing he has not long to live. Answers from legal representatives appreciated.