[Always *]

Well, a 2 and a half year relationship is a huge thing just to walk away from with no repercussions even if she was the one who ended it. I can pretty much guarantee that from experience. Some people can move on really fast (seriously, I've had friends get new guys within a month) but you can't just jump into a new relationship after something like that and think it'll be ok with a lot of people (cause some people don't trust as easily and take a while longer to heal), a lot of people have to take to new guys for a few months even before starting a new relationship even for the kinds of girls who are very loving and trusting and hate being alone. You can know a guy is wrong and get out of a relationship but for everyone who ever had the slightest emotional attachment to it they need to heal.
She really may just need some time. It may be just that with the stress of exams on her she is now cracking and areas of her life are taking the hit. She might be realizing now that she wasn't as ready to move on as she thought and is trying to back out. She really might like you though, which is probs why she hasn't flat out ended it. But to be honest if things like this are happening so soon, it sounds like your a lot more certain of her than she is of you and that it isn't very promising.
But needless to say, just give her time, she'll come around when she is ready and decide what she wants to do.