My daughter has worn both and much prefers the Rip-it due to the increased visibility. There is a thread that discusses the benefits of each and some other alternatives.
Does anyone else she knows use a mask? Maybe she can try it on before you buy? I'm with amanda, this like choosing a bat or a glove can be a very personal thing. While some girls prefer one brand, yours might do better in another. But if you absolutely can't try more than one before you buy, I'd probably go with the Rip-It since "most" players seem to like that one over the GameFace.
Also, if you find a place that carries both you might be able to order online, then return the one that she doesn't like. However, that wouldn't be as great as trying out another girls. Just putting it on can be totally different from actually playing softball in one.