A couple of place to try: www.passportamerica.com click on discount parks. Good Sam may be able to find you a park.
As others say talk with the hospital they may be able to make some arrangements for you.
Wait until the weather breaks after she is allowed to travel and make a run for the south. Most major interstate highway are open and clean within hours of a storm. You could stop and hold up in say Wal-Mart or other large lots. If you hug the coast I-95 you should not have much trouble going south.
If your compartments basement are heated you will be ok all the way south.
God bless your wife for her help for her sister.