Well, unless everyone else is lying to you, I would apologize to her and say there is nothing else you can do since she is the ONLY one who has a problem with it. However, I have found a water and vinegar solution helps get rid of the cat urine smell. Double-Oh liked to use our dirty laundry as his litterbox (eventhough his box is cleaned daily) and we would have to put cups of vinegar in every load of laundry for the longest time.

But honestly, how did she bring it up? Was she rude about it? Was she being sincere? You can not help that she is so sensitive to smell. Perhaps go visit her instead of her visiting you if she can't stand the smell?? You can only do so much for her. After all, it is YOUR house.