I agree with the review on the cover (though I hate it when books have reviews on the front cover) that this story is reminiscent of C.S. Lewis' Space Trilogy. However, that trilogy might be my least favorite of Lewis' and I like this book even less. It was boring and Kate was annoying. Don't be rude to people who risk their lives to help you!
Barron created some alien species, but there was some confusion as to how much they knew of our planet. If I recall correctly, Ariella has not heard of Earth, but she says at one point "On your planet, you might call it...", which wouldn't make sense if she doesn't know anything about Earth. There was also an explanation of rings as being bracelets for fingers, but how could Kate expect her alien friend to know what a bracelet is if she doesn't know what a ring is?
The characters can also, at times, read each other's minds and I wasn't sure when exactly that was possible and for whom, so that got confusing.
I'll end on a positive note by saying that I really like some of the names in this book, like Ariella and Trethoniel.