Should I ask my brother's wife to be a bridesmaid?

My brother and his wife got married a few months ago and I was in their wedding as a bridesmaid. The problem is, me and his wife are not close at all. In fact, I knew her many years before her and my brother met and I've always had a rough time with her. For example, my mom and I threw her a bridal shower because she gave my mom a sob story about how "no one was doing anything for her." A few hours before the bridal shower, I happened to be on facebook, where one of her friends posted a bunch of pictures of her bridal shower (she apparently had one weeks before this second we one were throwing and failed to mention that). But this is really minor in comparison to the inconsiderdate and bratty stuff she constantly does. My mom says that I MUST ask her to be a bridesmaid in my wedding, but I thought this day was about me and my soon-to-be husband, not some spoiled brat. Furthermore, my fiance's sisters will be in the wedding, but we aren't asking their husbands. I think its only fair to have my brother and not his wife. Lastly, we are trying to keep the wedding relatively small, and I already have three close girlfriends that I want to be in the wedding, along with my fiance's two sisters. Please help!! I need to get my mom off my back and I think if I get some good responses, she just might let it go. Thanks!