The hotel gets a very minimal return from MR for standard rewards, basically I believe enough to cover housekeeping. I've seen folios at check-out where as little as $11.00 has been charged. But I believe hotels are contractually bound to Marriott to alot a certain number of rooms to Standard Rewards. So, if there is a no-show, the hotel loses the ability to sell the room to a paying customer, and isn't able to collect from MR. Thus the reason for the guarantee. I too have never, not cancelled" a room. But I would also speculate MR is not required to refund points, especially when they find out you gifted them, but left in your name. Sounds like your daughter needs to learn a travel lesson.