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Well, to be honest, she is defeating the purpose of what she is trying to do. Ammonia will attract cats, not repell them. To a cat, ammonia or bleach smells like urine and they will continue to go where they smell the odor.
If she is trying to keep them out of a certain area outdoors, she would be better off getting a motion activated sprinkler system
these are very effective and safe for all animals.
Please let me know if I can help further.