Am I entitled to demand the money I gave my mother to meet her needs, which she then took back and refused to return to me?

It is permissible for parents to take from their child's wealth under certain conditions. If the mother took the money for her need according to these conditions, then it is her right and cannot be demanded back. If it was a donation, then it is not permissible to revoke it. However, if it was a loan, she must repay it when she is able, and waiving it is an act of righteousness and kindness.