Maybe it's Time (a Horse Story)

Monica has been best friends with mean girl Rhiannon all her life, riding and competing her pony Buzzy alongside Rhiannon and their two other friends Stephanie and Isabel. But Rhiannon's little group is suddenly thrown into disarray when new girl Tui arrives at pony club. Monica is left feeling confused. Should she join Tui or stay with Rhiannon? But when the Rhiannon vs Tui battle heats up and Rhiannon tries to sabotage Tui and her pony, Monica's had enough. But Rhiannon is out for revenge, and she knows that the best way to get it is to target the most important thing in Monica's life.... Buzzy.