it sounds as though youll have to wait to go back to see her again. Theres got to be someone who knows her in college, you could get her emial/number off them. If shes quite hot its impossible for her to have no mates to get in touch with. It doesnt matter if you dont properly know the mates. If you just see her hanging round with some remember their faces and pull them up when you cross them and ask for her deets, she'd probably get the message that way anyway.
You could just straight up ask to take her out for a drink/dinner or whatever, just asking that question straight has served me well, but then i spend the next few days crapping myself about where to take her/how ill act. If you make friends first you might come across as a bit of a creep later on, so id say its best to just come across that your interested in being more than friends to start with.
do you want to get some practice in with other girls over the hols or are you only interested in netting her? You could just find out what works for you by practicing on girls over the hols and then just use that to get her in college.
i was in your position not making many female friends when i went to college due to having a girlfriend. Its the double edged sword of turning up with one really.
isnt her email on myspace?