Becoming

should be in nonhuman

I think it would have been better if it were in non-human. I think it might have been caught by more who like this genre.
I enjoyed the story b/c most 'shape-shifter' stories are about werewolves. I do feel like the whole story wasn't told. I'd have liked to be there for her first shift and see how they both felt and how it was for her. I would have liked to know more about their relationship. You still could do it, start the next chapter with her thinking about their life together. I would love to see you write more of their story.
In the future, I'd recommend getting an editor. The best writers on this site have one or more. That way the reader isn't distracted when they see small errors. It was a good story and I hope you keep writing!