A FlyerTalk Posting Legend
Join Date: Jul 2002
Location: MCI
Programs: AA Gold 1MM, AS MVP, UA Silver, WN A-List, Marriott LT Titanium, HH Diamond
Posts: 53,012
That shouldn't be a problem. 99% chance you won't be asked to show the card anyway. 0.99% chance they ask for the card, but don't bother adding her name to the reservation because, frankly, they don't care. It's a marketing promotion - nothing really more than that.
If the hotel insists on adding her name to the reservation as Guest 2, they can certainly do that without affecting the reservation and points-earning ability.