I'm going to take a guess and speculate that she has an exposed fastener roof system. You would be better off replacing the fasteners with the next size larger screws. The problem with exposed fasteners is, metal expands and contracts, a little more than an inch over a hundred foot run. The movement of the metal causes the whole to enlarge. This action coupled with the deterioration of the grommet on the screw causes leaks. Coatings need to be applied over a clean, rust free surface and can be a lot more expensive than installing new screws. Either option will have to be repeated again in the future.