My wife wants my mom to like her

My wife wants me to help my sister out with her son's medical bill because she is hoping it will make my mom like her. My mom doesn't like my wife but it's not because of anything my wife did. My mom doesn't even like me. I only associate with her to talk to my dad but she has made it clear I'm not her favorite kid. My sister's son got jumped and had to get stitches. She has made posts on Facebook about how her poor little baby got jumped for no reason and the er bill was like 700. We are well off and she said we should cover it. Maybe it will make my mom like me. I don't want to for multiple reasons. 1. My sister is an awful person and I hate her. 2. Her son wasn't jumped for no reason like she's saying. She's saying the bad kids beat up her son for no reason and he's a victim of bullying. No. He tried to force himself on this girl at his school which is why he got suspended and in his first day back the brother and his friends jumped him and beat him up. Maybe it's wrong to jump someone but she's seriously "He was beat up for no reason! My poor baby!" My wife wants to do this. I told her I don't want to and it won't make my mom like her. My mom doesn't even like me and now she's upset. I'm not helping my sister pay for her medical bills for her son who did something really bad hence why he got hot beat up. Am I wrong?