The obvious solution is to mount the sign on the roof of her car when it's parked in the driveway and take it down to store in the garage when she goes for a drive. Once it's on the roof of her car, it's no longer a sign on her property but a sign on her conveyance which doesn't fall under the association charter (unless her car is a boat or motorhome).
I'd wager places like this prohibit parking in your driveway or leaving your garage open or farting without a formal waiver from the association.
Them folks is nuts.
I wonder how they would react to a vehicle with vinyl or painted signage on it, such as a vehicle that advertises your business. Would they insist that you can't drive your business vehicle home and park it in your driveway or on the street in front of your home, because it constitutes a 'sign'? What if your business is a nonprofit Support Our Troops organization?