Can a person have an allergic reaction to cat dander after a cat has been in his/her yard hours before he has?

My neighbor is claiming she has an allergic reaction to my cat even though he or any stray cat may have visited her yard hours prior to her entering her yard (and my cat is no longer there, but inside or in my yard). Is this possible? She was hospitalized and is claiming her allergy was due to cats (mine? I don't know.) Years ago I was outside with my long haired cat and I offered to bring her inside, and she said she was fine as long as she was outdoors. She even months ago was on her hammock on her deck and we apologized for my cat, who was there, and she said that was okay, and that he could remain there. Now she denies that. I always supervise my cats and try to bring them back in my yard. A stray cat has been living under her deck at night. My friend and I hear it meowing at times. Outdoors, can a cat leave behind allergens hours later and, can she be allergic to them at that long time lapse? I always had cats outside with me in my yard in the past and she never complained about it until now.