If she was past the 14-day return limit, she wouldn't have been able to take it back without a 15% restocking fee. Do the math--for a $1500 (before taxes) laptop, that's a $275 fee (before taxes). She might have thought she'd have a better chance of recovering her money through Craigslist. As for why she'd return it at all? Buyer's remorse, need for cash, change of mind...the possibilities are endless. What's clear is that the only we she'd have a hope of getting her money back without going through Apple would be by selling it to someone else, which is what she did. If she wasn't past the 14-day limit, she might not have been aware of it (not many people are, to be honest), which could also have driven her to explore other options. At any rate, the deed is done. Time to move on, no?
Well since it was bought from a uni store, we don't know if the same 14 day restriction would apply. Also, if she bought it at $1300, the 15% fee would still leave her with $100 more than what she sold it for.
EDIT: The laptop was purchased on 12/11/07 (according to the OP's OP), and the OP reported to us that he had purchased it by 12/17/07 (the first day of the thread). This means that the girl was well within her 14 day return period, and would have lost NO money, since the box was unopened.
Once again, something does not fit.