OP, you should be really proud of yourself for taking a VERY hard step and walking away from a huge part of your life.
It sure sounds like this trainer has some issues⦠maybe a touch of a personality disorder of some sort. People with narcissistic personalities can be INCREDIBLY manipulative, and often engage in certain relationship dynamics that really wear the other person down, over time. A child/teenager navigating a relationship with a narcissistic coach? Thatās going to be BRUTAL, unless the parents are constantly in the middle of the situation, monitoring everything the coach says, and constantly enforcing healthy professional and emotional boundaries. Iām not trying to judge your parentsā role in this situation⦠I just am observing that if you are dealing with a coach like this⦠the experience will not be positive or healthy unless a VERY assertive, VERY involved, VERY aware parent keeps a close watch on the coach all the time, and constantly corrects inappropriate behavior. If that isnāt happening, a narcissistic coach will inevitably emotionally steamroll teenaged athletes. 
It sure sounds like this trainer has blown past important emotional/professional boundaries when interacting with you (a teenaged student) over the years. Thatās not OK, and not your fault. Please donāt blame yourself for not identifying unhealthy dynamics earlier! You are not even an adult yet, and you were a young teen when you first started riding with her.
Counseling might be really helpful for you in the aftermath of this situation, but if you are feeling overwhelmed right now, donāt put extra pressure on yourself. Same with SafeSport reporting. Take care of yourself first right now (gentle hug). Talk to your parents. You can do counseling in a few months, or whenever the time is right for you. For now, Iām just glad to read you are talking with friends and trusted adults. Thatās really important⦠abusive relationships can be very isolating. I hope the start of school also offers some important structure and balance to your life right now - these final years of high school ARE important, and itās totally appropriate for you to redirect focus to grades and college applications. Thatās incredibly stressful in and of itself for someone your age!
So keep your head up, keep on talking with the key support people in your life, and please donāt blame yourself so much for this situation. Hopefully, as this chapter of your life closes, a new one opens, and you will have new riding opportunities with a different barn and coach, that are much more positive.