Rejoice with Me, Sonrise Stable Series, volume 7

Summer camp is over and Rosie and Carrie are working to get their horses in shape for the state 4-H competitive trail ride. The girls are surprised to learn that Abigail, the arrogant new boarder at Sonrise Stable, is also entered in the race. Can Scamper and Zach keep up with her flashy Arabian? How much is Rosie willing to risk in order to beat Abigail and win the competition?