I'm closely monitoring one of my common leopard ramshorns. Somehow it managed to get INSIDE the veggie clip... the zucchini fell out the snail got trapped. I rescued it but it has a crack along it's shell... seems to be acting normally- but I feel bad and nervous for the poor thing.
Put a bigger shell in there for her. Maybe she left her old shell cause it was too small? I don't know anything about snails so just guessing. Hopefully, one of the snail experts on here can help you.
The most humane way is to take the snail in a small cup of tank water and put it in the freezer. As the water gets colder, the snail basically goes to sleep. Once the water is frozen solid, there is no chance the snail is alive. Discard snail and ice in the trash.