Some people handle being busy better than other people. You sound like the sort who handles it very well. Maybe your friend isn't as good at it as you are, though. For my part, I don't handle being busy very well, and when I'm overwhelmed or I feel like I've been working like a dog, I go through bouts where I just don't want to interact with anybody, even my friends. It has nothing at all to do with my friends' personalities. It's just an effort for me to interact with others--even when I really like them and have known them for years--and when I'm very tired, I have a lot of trouble working up the energy to make it. I don't know, of course, what your friend is like from what you've said, but I don't think her being "busy" shows that she's a bad friend worth dumping. I'd think she's just working hard, tired, and maybe a little overwhelmed from adjusting to a new school.