No suggesions to stop spraying. I don't think its a medical problem because of all you described. Do you let your cats outside? If not I'd put around a few plants you can by at plant stores often labeled as Cat-be-gone, I forgot the regular name but you could ask a worker at a plant store. I'd also head to the pet store and look for cat repellants that might work outside. Clean the area where the cats sprayed real good and maybe block off that area in your house for a while.
If it were me in this situation I would humanely trap the cats and bring them to a shelter. It should be legal to do in your area also. Have you confronted her about her cats spraying your yard and house?