This is a follow up my "Creaking Cranks" post of a few weeks ago. I took her to the LBS and got it looked at. Turns out there was something loose in there like a bearing or something, the whole crank could have slipped out but it didn't. So now it's perfect again. He also fixed the buckle in my wheel and various other jobs, so, all problems solved for €35.
The moral: it's probably not as bad as you think, just take your bike to the shop!