Does she have your address, @Martha232, or is she asking you for it?
First thing is to go to your dashboard and find "All reservations". Click on that and check the list. Her first name may appear with "Cancelled" beside it, which will mean she tried to book but for some reason (payment being most likely) the system didn't allow it and she only thinks she has a confirmation code.
If she does not appear at all, and it really looks like she is booked because she has your address, etc., give Airbnb a call or tweet AirbnbHelp on Twitter and get them to look at it.
I would say if she does not appear on the list, and she does not have your address, she should be the one to call.
Will you let us know how it turns out?