Zoe's close relationship with her mother and her sister, Rosie, is especially nice to see, and she does still talk to her father via Skype, which is a reality with which many children have to deal. Jade and Becky are fairly stock characters, but Mia is quite sympathetic even though she isn't always nice. It's a pleasant change to see a rich, mean girl portrayed as a human being rather than just a literary device, and it speaks well that Zoe tries to understand the other girl's perspective.
Horse stories have a small but steady fan base, and it's always good to see a new one. Jessie Haas' Rescue is one of my recent favorites, and I love Hapka's Ponies of Chincoteague series. Free Rein, with it's wonderful Raven, will be a big hit with readers who either ride horses or would like to, and who also can get their teeth into a good mystery.