Could be injuries? Could be fungal? Could be parasites? One thing's for sure, I wouldn't put her in with the other frogs until you know for sure what's causing this.
https://www.thespruce.com/frog-lumps-1238194
Here's a post on the subject. It's not terribly helpful though: http://www.frogforum.net/showthread.php/7837-Brown-spots-on-green-tree-frog