Rather, she didn't suppose the problem was with the device. The Time Turner itself did very little except process her request, similar to a train ticket. Just what happened after she showed her ticket was up to the driver. The driver apparently decided that it would not move her the hour and a half necessary to make it to Muggle Studies, but instead a whole fortnight. That first time, as far as she could tell, was just to show her that it could happen. Unless she'd inadvertently fulfilled some purpose, which was also entirely probable. Once she got past the first few weeks of panic, her academic nature urged her to follow whatever path time led her down. Something told her that very few, if any, had gotten as far as she had.