I empathise. My partner (don't live together) has a daughter I really don't like. A selfish, attention seeker, who uses her dad and gives him little in return. She was deeply unkind and viscous to me a couple of years ago. I can't forgive it.
But. He loves her dearly and she lives with him so I have to tolerate her. I try not to interact with her much when I see her, try to be busy with something so even if I'm in her company we are not interacting much. IF I can without appearing blatantly rude, I go to another room.
He talks to me at length about her at times. I try not to be negative. If I can't be positive, I reply with an mmm or ah or just a nod.
If I know in advance she's going to be around, I plan to be away, doing other things. I do mostly what is best for me.
Ultimately, after the big scene where she was so viscous, I decided that by being angry and hurt I was the only one suffering. She isn't. She got her own way, so is fine. He isn't. He has her around and is happy. So I resolved to let go of my feelings. I didn't manage it totally, but I do feel a whole lot better than I did.
But no going back to 'nice' family events / outings etc. I just won't do it if she's there.