It sounds like your friend might need a friend. You said she seemed stressed so maybe she is having a really hard time. She may not even realize she is being such a bitch. Maybe the next time you see her, you should just tell her how you feel about her remarks and ask her if she needs to talk?
A lot of times when people are very insecure or troubled, it comes out in their behavior in negative ways eventhough it is not what they intend.