I have had several jumping horses over the years, and except for my TB, I have used a crop on every one of them. I do not believe that it is bad if you need to tap their butt with a little more force sometimes, as I have had a couple horses that really liked to test the rider, and see if they could get away with running out or slamming on the brakes, but I have never left lines, either in the hair, or on the skin. I have noticed that often times, it is the sound alone that wakes up a horse, and gets him/her going nicely, not the actual contact of the crop and their body. I personally would first try to talk to her, suggest some things that you've done when your horse maybe refuses, or balks, and if that doesn't help, and she continues along these lines, get an adult in charge, such as a trainer, the barn manager, ect. And tell them what you've been seeing, and show them any pictures or videos you may have, so they can see that you aren't making things up. Hopefully she stops before she does any serious damage to the horse. Most horses I've ridden have tried to refuse a fence at least once or twice, but if they are just learning, reassuring them, and gently coaxing them, even lowering the fence to help gives them the confidence they need. If they are well trained, and normally don't refuse a fence, then that is when I believe that a harder tap might be necessary, only to put them back in line.