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Well, I'm going to suggest what really needs to be done is just what you wanted to do in the first place, open up her ceiling. At this point that's the only way to find the source her leaks since all other attempts have failed. It's not clear to me if nothing in your bathroom has been used for several weeks. Please clarify. If your bathroom has been used in the interim I have a few possibilities. Also I need to know if your tub/shower in that bathroom is tile or fiberglass.