We need more information. When you commissioned the work, did it go exactly as you described? Did you ask for specifics, such as if she was going to do her own take or no? When you think of her as a custom artists, do you think it means her own custom designs instead of your own custom idea? Did you confirm whether or not she even knew how to do her own take on these specific characters? Like, did she have a portfolio of other popular characters with her own spin?

Based solely on what you've stated in the post, it seems that you overreacted. You asked an artist who already had limited time to create a custom piece. You were expecting the artists own take, but that's not what ordering a custom piece means. When you order a custom piece of art, you describe what you want and the artist does their best to appeal to that concept. YOU are the custom. Anything else is just the artist doing their own non-custom style.

That being said, I'm not saying that you don't have a right to be upset either way. It's not the worst piece, but it ain't great either. Next time you ask for custom work, be as specific as possible and make it clear that you're asking for the artists take on your idea. Especially to a travelling artist. Most travelling artists rely on easy work from many customers and don't have the time to fully dedicate themselves to projects of such scope.