Manual for mother in law + people pleasing

Hello! My husband wants to please his parents by going on a long weekend trip. He says his mom has been sad and needs to go out somewhere. I personally dislike some of his mom’s behaviors and haven’t worked on accepting those behaviors 100%. So, I feel angry at her and sometimes resentful. I wish she was different. The problem is I don’t want to go on the trip because I don’t like her behaviors. I haven’t said no because I don’t want everybody to think bad things about me (people pleaser). Also, she doesn’t have these behaviors all the time and I surprise myself by feeling comfortable and joyful around her. What should I do?