Should my brother's fiance have asked me to be a bridesmaid for their wedding?

I'm his only sister and usually the bride asks the grooms sister or if he has more than one she asks the one she's closest to to be one of her bridesmaids to kind of mix the families together. I know it's completely up to the bride but that's what most people do. Whenever someone finds out my brother is getting married every single person always asks me, "Oh, are you going to be a bridesmaid?" And then they're always shocked when I say no. They even think she doesn't like me. I know it's up to the bride but it's pretty much expected and I think it's really rude that she didn't ask me. My mom and I don't know anything about the wedding. The bride is supposed to invite her soon to be mother-in-law out to brunch with her parents and to come with her to pick out a dress and whatnot but she didn't do any of that. We're pretty much just guests. We'll show up and that's it. Do you think it's rude of her not to include us? I know she does these things with her mom and sister and bridesmaids, but not us. And truthfully, I don't even think she likes us. She never invites us over. If my brother does she always vetoes it, and whenever he comes over (which is extremely rare) she usually stays in the car. If she does come in she doesn't make conversation. They've dated for 5 years and I barely know her. My brother says she's just shy but my mom and I think she just doesn't like us. What do you think? And do you think it was rude of her not to ask me to be a bridesmaid?