Whatever state you live in, you probably have a 'limited liability act'. Forty six state have such a statute.
Google " 'Your state' equine limited liability law'. Several websites will come up with every state's limited liability law. They will be listed in alphabetical order if you scroll down or there will be a list of states to 'click' on. They spell out your responsibilities and hers as well as exclusions.
When I trained for the public, I spelled out to people (in a contract if I did not know them) that it was their responsibility to come and ride the horse under my supervision before they took the horse home. I also told people that too much feed and too little riding and exercise would likely be a problem for their 'green' horse. This can be a problem for even an older horse.
DO NOT contact your insurance Company. They will probably cancel your policy or raise your rates unless you have a specific 'activity insurance'. Then it is not going to cover her getting bucked off anywhere other than on your place. The less you ever say to an insurance company or agent, the better off you are.