She needs to come OFF the barrels until the problem is fixed. Smrobs' "general" advice is good.
Your horse does NOT need to be running right now. She needs to be learning subtleties and softness. Get her riding off of your seat and legs, not your hands. The reins/bit are not the brakes. They simply allow for ease of the rating cue.
When you do, eventually, after a lot of re-training, come back to barrels, start with slow work. Make her trot up to the barrel, stop (on a "whoa" and sit-down command, not on a yank of the reins), back up, and wait. Do a rollback in the opposite direction if you have to to get the point across. Then walk around the barrel, trot to the next one, and repeat. Repeat the whole thing at a lope, too. Don't allow her to anticipate or to rush. If she stops rating and starts going wide, slow her back down and reinforce her stop off the seat again.