This book by Australian author Kate Forsyth is the first volume in the series Rhiannon's Ride. Some years ago a friend introduced me to the Garth Nix's Old Kingdom trilogy which I enjoyed and recently a library patron recommended, when we were discussing fantasy, the books of Kate Forsyth.
One Horn's daughter is unlike the other satryicorns. Her father was human and she had not grown horns, important distinguishing features for satryicorns. She knows that she needs to escape the herd if she is to live so she captures a winging horse and manages to flee the mountains to a new life. This is just the beginning of the adventure as she joins a caravan of witches and apprentice witches as they head to the Tower of Two Moons. During the journey a decision is made to travel via a shorter route via the remnants of the Tower of Ravens, a dangerous area haunted by the dead and the nearby castle lauded over by the Laird Malvern MacFerris and his sister-in-law lady Evaline. With Lewen's help Rhiannon manages to survive the journey and discovers that she too has special powers, not only over horses but the ability to use stronger magic.
I look forward to reading the other two books in this series and also the books in the earlier series - the Witches of Eileanan.