Still a terrible plumber

My daughter has a three piece tub/shower. Along the outside edge, where the top and bottom pieces meet there appears to be some water damage to the drywall. This damage appears to form a half circle in the drywall with the edge of the tub/shower seam at the center. Many months ago I tried to caulk between the upper and lower pieces to see if that would help, but the bathroom caulk I used didn’t hold. Any ideas on how to fix this. Photos attached. Thanks.

take the door rails off and seal it the crack. When the panels where put in they should have squirted a bead into the deep bowels that joint of that outside edge.

Thanks Krazidav. Any particular sealant recommendation?

I as DAP.
water clean up.
silicone has to be CLEAN and it's messy

Great. Thanks again.