Mercedes Lackey writing a Western? With zombies? I had two simultaneous reactions: "This I gotta see" and "I doubt that'll be good."
It wasn't terrible. It was okay. Mildly entertaining, easy to read, no thought or familiarity with zombie or western traditions required, even though the three main characters do seem to have stepped out of different genres.
Jett, the first and to me most sympathetic character, is the historical romance protagonist girl-inadequately-disguised-as-a-boy-to-search-for-her-brother. That's her on the cover, with the boobs. She is fiesty but secretly longs for her old Southern Belle life of pretty dresses and cute boys. She is from New Orleans so she can conveniently explain all about zombies to the other characters.
Honoria is visiting from Steampunk land. She is genius-scientist-girl-with-no-people-skills. Although she doesn't realize it because she cares only for Science, she is gorgeous, so everyone likes her even though she is rude and annoying.
White Fox is our Western character. He is wise and calm and good with horses because he was raised by Native Americans. But he is ethnically white so it is okay that white girls are attracted to him. He gets the least character development and is mostly in the story to be helpful and competent and good-looking. Otherwise Jett and Honoria would have to spend too much time doing practical stuff to survive, plus people might suspect they were lesbians. If there were any other people around, which there aren't.
This is a fun, quick read and will probably appeal to teens who haven't read much in these genres or want to avoid extremes of sex, violence, scariness, etc. But it is pretty fluffy compared with the dark and intense fantasy westerns of Gemma Files or even Cherie Priest.