I have a friend who is a girl. And lately she has been getting really bitchy. What should I do?

We used to like each other a lot, but are just friends now. It always seems to be over stupid stuff too! It's defiantly not her time of the month or anything like that because it has been happening over multiple weeks. I always try to avoid being a ***** back when she does it. Should I confront her about it? If so what should I say?