Well, as always seems to happen with mystery illness threads, my poor little frog passed away some time in the night. I'd still like to know what it was and if anything could have been done. I couldn't find anything when I was searching the internet so perhaps this will be able to help someone else that comes across this thread.

Update: I'm not going to do a necropsy, but since she isn't in pain anymore I tried to get a better look and more pictures. The pictures don't help, but it is not a hernia. It's a sac of some kind that feels like semi-hard gel. It was squishy but tough, if that makes sense. And whatever it was, it definitely tore a hole in her side. I was able to pull her skin back from it, so it had to be something inside her, one of her organs perhaps? . Anatomy pictures aren't helping.