Someone on deviantArt is saying that they stolen an adoptable she created and put it on a book item, but she hasn't said which adoptable/book it is yet
Looks like I got a response!! Wow, this item is really old. So Tumblr user krystallo made some adoptables way back in the day, and although the original Fire Gelert image has been lost to time, she found her Faerie version.
And TNT used the Fire one in the item Fire Pet Guide. Here it is:
Like there's no mistaking it, that's definitely her Gelert there :V And this item was released all the way back in 2008 too!! She said she didn't contact TNT about this though. Now I really wanna know if they've stolen more fanart for their items hahah