It sounds as though she makes a habit of doing this sort of cheating. You are not being unreasonable, just taking your responsibilities as a cache owner seriously. I would ask her how many other caches she has logged as found which she didn’t find. One of the main reasons for DNFs is so that the CO gets an idea that a cache may have gone, but even if it has it still shouldn’t be logged as found.
This is what Groundspeak say “As the owner of your cache listing, your responsibility includes quality control of all posts to the cache listing. Delete any logs that appear to be bogus, counterfeit, off-topic or otherwise inappropriate.”