Yep, sounds like she did a "restore". IE, wiped the drive and re-installed the thing as it was new. Yuck.
Problem is not only did she erase the drive, she likely wrote data over top of some of it.
It could all be recovered certainly. It's a question of how much it would cost. If you really want that data, tell her to stop using the machine... shut it off now. Then look up data recovery services in your area, and see what they would charge. This is likely an easy one, since the drive is not burned or destroyed. The price could be reasonable depending on the situation, although it depends what the data is worth to you.
Oh yeah and buy her a CDRom Burner to back up that important data on in the future!