Used book – An Amazon at Pin Hollow, Bonnie Bryant, Catherine Bard-English

Max has a surprise for the students of Pine Hollow: Emily, a new recruit, rides side-saddle! What's more, she knows an incredible amount about horses. Carole, Lisa, and Phil are captivated. As for Steph, she's simply jealous! To please Phil, she tries to be like Emily. She changes her look, practices side-saddle riding... Her friends are perplexed: where has the real Steph gone?