Sponsorship I-864 and payments

[casablan1]

Hello. I sponsored my ex-girlfriend's adult child (22 year old daughter). I signed the sponsorship form I-864 in early 2014. I signed it reluctantly after they begged and pleaded with me to do it. I told them, I did not have enough money but I caved in. They said it was just so she could stay. Her mom is working on becoming a citizen. At the time I signed to sponsor her, we all lived together. We have not lived together since shortly after I signed the sponsorship. The daughter I sponsor now lives with her boyfriend. I had been paying the daughter 800 a month to try to help her. Now she wants it increased to 1,100 a month or is threatening to sue me. She also gets a small amount of money from her son's father in Germany. I really don't have this money. Do I have to pay her? Can I just offer her and her son to move in with me? It would save me money to have the daughter live with me. I am sure she would say no, because she does not want to leave the beach area and just wants the money I pay. Additionally her mom, had really master-minded the whole thing. She talked me into the sponsorship and reportedly she had a home in a European country and was going to be the primary sponsor. I thought I was sigining as the back up sponsor but I was the only sponsor. I had signed the form and the mom took it to the lawyer, so I never saw the whole form. I don't think her mom has any money in Europe but she just acts like she does. It really turned out terribly.

I really don't mind helping but I feel like I am being taken advantage of. There is almost no information on my rights, that I can find.

Do I have to pay her money and will she win if she sues me?