Am I wrong for not wanting my MIL at my wedding?

I feel awful for feeling this way but I just want my wedding to be perfect. My fiance's mom is extremely mentally ill. She rarely ever even talks. She currently lives in a home for the mentally ill. Trigger warning of sexual assault.

My fiancè and his 4 siblings have the same dad as his mom.... She was assaulted by their dad when she was about 6 and it continued for years. He was born when his mom was 14 and he remembers seeing his dad/grandfather take his mom into the room and could hear him assaulting her. He's dead now thank God. But his mom is permanently messed up.

I've met his mom a handful of times and she doesn't talk much. She has never said two words to me. She's completely lost her mind. She will need someone to basically babysit her at the wedding. One of his siblings will do it probably but I feel like my fiancè will be too focused on his mother. Plus she just makes me sad. I know that's selfish but I don't want to be sad at my wedding. All she is is a reminder of my fiancè tragic life and upbringing. Our wedding is supposed to be a celebration.

Edit: He does want her there which is why I feel shitty. He doesn't get to see her much because the home she lives in is so far away.