How do I stop being friends with someone I don't like?

I have this "friend" who I've come to realize is really not a nice person. We are part of a group of girls and we've always been relatively close among each other. Lately I've been noticing more and more how she continually puts all of our friends down with rude, snide and/or insulting comments. My roommate (part of the group of friends) has noticed this as well and feels the same conflicts as I do.

She was part of the "popular" erm bitchy crowd in high school and I feel that she has brought this attitude with her in college (second year here and still the same). She feels the need to make others feel bad about themselves by self-righteously telling them what they are doing is completely stupid (when it's not necessarily).

I don't really want to be friends with her anymore, but she really has no friends outside of our circle, lives near us etc so I feel like we're "stuck" with her.

So Reddit, what do you suggest I do?