If I understand you correctly this was a built in place shower stall. We replaced one last year, yes it is a pain in the . I don't know if this is the same but what I had to do is remove all the tile, masonary and the mesh wire behind it, to the studs. This takes beating, pounding, prying, I would recomend eye protection for this. After it was removed I checked all studs for water damage and had to replace about half, remove any remaining nails, etc. We replaced the shower pan then I went back on the studs with 2 layers of 1/4" hardi-board. We used roofing nails to attach, every 5". You can use screws but you have to countersink. Then tile. New shower door, etc. It was a mess but when we finished, it looked great. Of course we had some mud work to do and re-painted the bathroom. The owners were more than happy.