I'm single, but always request TWO room keys, I keep one in my wallet and the other in my side pants pocket--it's easy to leave your room key on a table in your room (say), walk out and be locked out, but the 2nd key "saves the day".
So in OPs case even if she were a hooker, couldn't he separately give her his extra key and if she were challenged by security in the elevator she would produce a valid room key.