I don't want my sister as my bridesmaid.
Do you have a particular reason?
She is stupid and she does not deserve to be my sister.
The way you talk about your sister is mean. She's your family so she is going to be part of your wedding. She'd be hurt if you exclude her from your wedding, and you would regret doing so when you are older.
I don't care about that. She called me ugly and thinks she is better than me.
Was it recent that your sister called you ugly, and do you think this is a lingering resentment that she has?  If it was a long time ago, or if it was just something said in anger, then you shouldn't hold a grudge.  Your sister will always be your family, so you should let her have her rightful place at your side.