sister is asking for money to bail her out constantly through my mother, what to do ?

Hi

I am a dude, working as a software engineer and making some good money and worked extremely hard for the money I earned, I never been in debt, work in restaurants, etc. and now I am a successfully software engineer in Chicago . Now, my sister all of a sudden is decided to get her second master in “art and design” from a very expensive university in New York. My sister is putting my mother under pressure to ask me for money and financial proof and paying little stuff here and there. The problem is, my sister is real jerk, over the past 6 years she NEVER called me to ask me how am I doing, the only times she called me was the times, she wanted something from me usually some money. I used to help her although a world class jerk but she is a part of family and I wanted to her because she is my family (although not optimal).

The real problem right now is that she wants to get her second master ( she has a bachelor in Fine Arts -> paid by my parents and I paid for my bachelor and master all by myself without any help or something, she also has a master in some design stuff and now, she wants to attend some real expensive private art university in N.Y.).

Under the pressure of my mother, at some point, I had to provide some financial form which would state that how much I got in my bank account and now, for the first of ever, they know how much I have in my bank account!!! ) but the problem is as I said, I am doing all these because of my mother. The sister is real B. She talks with my mother all day long and then my mother somehow convince to to provide these financial papers and financial help (so far, in the scale of about 800$).

The main problem is, the sister doesn’t talk to directly, doesn’t say thank you. doesn’t appreciate anything (not that I am looking for a thank you, no, but a simple thank you is better than NOTHING!), she doesn’t call me, she just texting me, happened a lot of times that I call my mother and she came and interrupt and doesn’t let me to talk to my mother, and a whole lot more stuff. The only reason I have to provide these financial things is the pressure from my mother. I really love my mother and I know she loves me but this whole thing is getting out of control, I am afraid the sister start asking for more and more and more ….

we are coming a middle class family, my father is around but doesn’t engage much in anything, tries to stay aside. My mother’s financial situation is pretty good and well off but nothing luxury.

Now, the question is what am I suppose to do in this situation ? because I am kinda desperate. Looks like I have been emotionally taken hostage. Anybody has experience in this type of situation? how should I politely refuse to help the sister (which clearly tries to take advantage of me financially and she is perfectly fine with keep studying art at the age of 30 for yet another 2 years), without destroying my relationship with my mother ? I know I cannot make everybody happy but I need a strategy to get myself out of this with minimum relationship damage with my mother.

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tl;dr : the sister is constantly asking for money through my mother, means she doesn’t directly talked to me, she goes through my mother and then my mother asks me for some financial thing. Looks like I am been taking advantage of financially. Any solutions?

thanks a lot everyone