Its good to find a guy, like myself, who actually cares about more than mindless sex
(not that thats not amazing)
I think not having credit is possible you know...since, even though she has a job that doesn't mean she will be getting daily cash - she could get paid every week/fortnight/month.etc., so three days isn't really too long - although i know it feels like an eternity when your waiting for a response. Anyway - i'm sure everyone here knows how quickly credit can disappear from you phone on a night out, one long call to a mate slurring down the phone about how much you've drank or how "your sitting still but the rooms still spinning" can solve that problem...or the even more conventional falling on it and leaving a 3 hour message in someones voicemail - bliss!
just give her a ring, and if you sound obscenely nervous, she is more likely to say no - maybe organise something for a few mates so its not just the two of you (although obv. you would like that), but then you can move from there - you should never expect to just walk str8 into a relationship.
also - given my experience of having to carry my mates back to college after they've passed out outside clubs, she wont be too pissed off they you did so, as its a kind and honourable thing to do. also, if she already knows that you like her, it will given her a check that your not just in it for the one night, and will have shown her your a more honourable bloke
either all that or, she just doesn't like you - but its better to regret something you have done than regret something you haven't done.
as you say, you probably wont be seeing each other day to day next year, so just go for it! it doesn't sound like you actually have anything to lose - if you saw her every day you should think twice because you dont want to lose a friend, but since you dont, you can always survive the occasional awkward, squirmish glance as you cross each other in the street.
but, yes, katies right...just call her!