**** sake, some people are WAY over reacting. I have plenty of friends who I enjoy hanging out with but I can only deal with them in small amounts. There are people in your life that you will want to spend every minute with cause you just have that sort of friendship and inevitably, there will be those friends who you like spending time with but only once every so often.
Unfortunately, it seems, your friend wants to spend all her time with you but you feel like you can only take little amounts with her - completely understandable. It doesn't make anyone a bad friend. In fact, you could argue that in order to keep the friendship, seeing each other every so often is a better way, rather than hating them because they are driving you around the bend.
I can see someone point of view though, at the end of the day, she is still your friend and you have to be happy for her, regardless of what university she will be attending. If it's the same as yours, you just deal with it. You nip it in the bud by telling her that you are really going to get into your studies and you could make plans for spending time weekly/fortnightly/monthly with each other.
It's possible that she will meet another group of friends, from her course and you'll find yourselves drifting apart anyway. If you live in different accommodation or different areas in the same accommodation, you'll probably find that you'll both make friends with your own room mates and you'll drift that way.
You're not a bad friend.