You are probably too clean for your shower's good! Most fiberglass showers and tubs are coated with gelcoat. This material scratches easily when scrubbed with abrasive cleansers. It is recommended that the surface be completely refinished with a new coating to give it the appearance and durability of a better-than-new fiberglass shower. Then to maintain the shiny luster, you may want to wax the walls about once a month with a liquid automobile wax to help prevent water spotting. Leave the abrasive cleansing powder at your mother's house and use a NON-abrasive liquid cleaner with "scrubbing bubbles" or other mild detergent.