This is so difficult for you. I have one son who is a winess and one who is not. I am lucky they are both very helpful and loving.
What about being totally honest with and ask what she thinks you should do. Is it right for you to give your hard earned money to someone who apparantly does not care very much for either of you. It may make her think. If she continues to show a disrespectful attitude I know I would not be helping her out very much.
That is me. You obviously have to decide for yourself. It's not easy.