hmm...see if they will let you add her to the DME, without dealing with the Boardwalk hotel issue. If not, I'd consider just arranging alternate transportation to the resort (cab, shuttle, etc) and just not telling Disney until you get there. I'm sure the Boardwalk will accommodate you once you are there.
the back up option would be to call 407-824-2222 and ask for boardwalk operations, then ask to speak to the duty guest service manager.
see above comment. i would do this same thing if you can not get her on DME. So she is in a cab or what ever from the airport to the hotel. big deal