I removed wallpaper in the bathroom, did a fine job prepping the walls and painted. Several months later I am having trouble with the drywall joint that runs along the top of the fiberglass shower stall, at the point just below the shower head. Moisture caused the drywall to start swelling and peeling upward a bit, away from the fiberglass shower stall and silicone caulk on the joint.
I had prepped this area carefully as it had been damaged under the wallpaper that I removed. I used joint compound to resurface that area after I removed the old corrupted sheetrock surface paper. I used paintable silicone caulk to seal the joint between the sheetrock and the fiberglass stall. I primed it thoroughly with a couple of coats of primer before putting on the top coat of paint. The caulk is still firmly in place but the sheetrock above it is failing.

The rest of the shower is fine, with the same treatment at the joints where the shower wall meets the sheetrock. It is just this area about six inches long under the shower head that is giving a fit. The shower head pipe comes out of the wall about four inches above the top of the shower stall.

A couple of questions about fixing this again. Would it help, after removing the silicone caulk and joint compound, if I used fiberglass mesh drywall tape to try to firm up the drywall joint area? Is vinyl joint compound the best choice for this application? What approach would you take to repair this permanently, short of tiling the shower stall? Thanks in advance for any assistance.

Replace the "drywall" with moisture resistant sheet goods like "green board" and use nothing but waterproof tape, mud (acrylic mud) and such in that area.

Whoever built the shower took the stupid let's save $5 route and used the slightly cheaper and totally WRONG materials.