Love is a Gift by Lauren Brooke

Heartland is a horse farm nestled in the hills of Virginia, but it's much more than that. Heartland is like no other place - it's a place where the scars of the past can be healed, a place where frightened and abused horses learn to trust again.

Amy and Lou are excited to visit their father's ranch in Australia. When they arrive, Lou immediately bonds with their father's new wife, Helena. However, Amy finds herself holding back. She avoids the farmhouse and seeks the security of the stables. Amy wants to reach the reluctant Spirit, a gray gelding that was trained by Helena. But no matter what Amy does, the horse won't let her in. Can working with Spirit help Amy to open her heart and accept her father's new family as her own?
 
- Goodreads Summary