Take lessons with your instructor and ride her show jumping horses in the lessons, assuming that comes with the lesson fees and you/your parents can afford the lesson fee or you work off the lesson fee. Ask her about showing them and if you could work off the amount it would cost to take them to a show and show them. You are going to have to save up money for entry fees and all that stuff though. You can also work off a ride on one of her horses, so in addition to a weekly lesson, you could also come out and practice on one of her horses so you are riding twice a week.
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown