I have heard it can take years for the cat allergen to clear a home!
If there is a spare room that your Aunt will sleep in, start keeping that door closed and the cats out. Try to vacuum the room well including wiping down the walls, draperies, etc. That will help reduce the amount of allergen in the room. Having you Aunt take an antihistamine will help, she should start a few days before arriving at your house. Bathing cats I don't think helps, but wiping down the cats with allergy wipes supposedly helps. Some people have a psychosomatic reaction just to seeing a cat, so it might be helpful to keep your kitties out of site just in case.