I have mentioned previously on this forum that this is a common problem I find in my "HandyMan" business, and there is a solution rather than pulling the tub/shower unit. This involves shooting something like "Great Foam" between the tub/shower unit's bottom and the flooring IF you can gain access to this area. This is not always easy, but a do-able project. Your daughter has now invested monies into this home and has to decide what to do before a crack develops that will leak water.