Go to the next show as an observer, and watch the other instructors coach their students. Hang out in the stabling area, the warm up ring and the in gate. Who seems organized? Whose students seem like they're prepared and enjoying the experience? Listen to the coaching - is it positive and encouraging, or borderline verbally abusive? Do the students seem to be know how to respond to the coaching, or just riding around hoping the coach stops yelling soon? Does the coach send the student into the ring with a plan, and review how things went when they come out of the ring?
If you see someone you think you'd like to work with, ask them if they're accepting new students. Have a candid conversation about your goals and your expectations up front. (This saves a lot of pain later, believe me!) If they don't feel it would be a good fit, ask them for a recommendation.
Based on your posts in this thread, I have to agree with LuvsJRT - you need another instructor. Some of the things you described seriously make me question her competence.
However, in the meantime, DO have a conversation with your current instructor about how you're feeling and what your expectations are. Try to keep emotion out of it as much as possible and pare it down to a 30 second commercial: "I was really unhappy with how the last show went. I felt rushed, unprepared and overwhelmed. I don't want to show again until I feel like I can get more out of the experience, and I'd like to come up with a plan for my lessons to get me there. Negative experiences and negative coaching really have an incredibly demoralizing effect on me; I need to know exactly what's expected of me and then be encouraged toward that goal."