It's hard to say what might be going on here Daniel. It could be that some ex-boyfriend has suddenly popped back on the scene. That could be the 'certain reasons she'll share one day'. You've only been seeing each other a week, so is it possible that she hadn't really finalised a previous relationship properly? That's happened to me more than once. It's really annoying, but there you go. Life's like that sometimes.
In any case, there's obviously something going on and it's probably nothing to do with you. I know it sucks, but if she is going to be eratic and/or if there's someone else in her life it's just as well to find out now before it goes any further. All you can do at the moment is to wait and see if she contacts you again. If she does, you will really need to find out what these 'certain reasons' are before you agree to move forward. Don't take 'no' for an answer if she tries to avoid telling you, whatever you do.
"The only thing to do with good advice is to pass it on. It is never any use to oneself." - Oscar Wilde