well, for one thing, PUT A BRIDLE on the darn horse if she is going to ride it. If the pony drops her head past her withers, your daughter needs to tug it back up and drive that pony forward. For another, get her some decent riding boots with a heel. This is a safety thing--just as much as a helmet. Next, teach her to listen to her horse's body. It's obvious when a horse is going down. I second carrying a crop, but I'd hesitate recommending its use until you know what the pony's response will be. A little buck might not upset your daughter, but if she blows up, that could get ugly. The point is that rolling can't happen if the horse is being driven forward with purpose. If the pony is ambling around the pasture without much direction from her rider, she isn't likely to think she HAS to be upright. Your daughter is going to need to be more aggressive.