I recommend bying a brown trench coat, and a smoking pipe.
Then get a large magnifying glass, and snoop around her dorm room.
j/k....
You can either,
A. Say nothing and hope it gets better (not recommended)
B. Talk to her (recommended)
C. Consider the fact that she could be, uh, you know...moodswings...etc. etc. do I have to make myself any more clear? *uncomfortable stare*