Being the better person does not mean you have to subject yourself to disrespect and more abuse. The whole situation just makes me sad. On whether I would go or not, the fact that your family had plans with you and then changed them without consulting you...That would make me feel unvalued, loved, respected; and it would be a big reality check / heads up that this is how they will treat you and expect you to take it because they place your sisters feelings and love above yours. (My impression from reading is that your (mean-sister isn't the one wanting to makeup, but that your family wants to pretend everything is all good for the holiday.)
I should probably delete this post, but I think you should only go if it's what you really want, while realizing that things are going to be the way they are. :grouphug: