Unless Marriott rules have changed, book them in your account with points transferred from her account.
To book the room, you can call up the Marriott support center and transfer Marriott points to cover the award. You can transfer enough points up to the amount of the room (in this case, 80,000 points). You could even transfer the full 80,000 points EVEN IF YOU ALREADY HAVE ENOUGH MARRIOTT REWARDS POINTS IN YOUR ACCOUNT ALREADY!
How to combine and transfer Marriott points (for free!)