As has been said-you have tried the "ask nicely" route, and apparently she didn't get the message. IMO you have limited choices. Either get blunt with her and be REALLY CLEAR that she is not to touch your horse unless there is some life threatening emergency such as, heaven forbid-the barn is on fire, or-move. Period. Not open for discussion, and you owe her no explanations. I would also make the BO well aware of your request so that the BO can insure that this wanna be trainer keeps her mitts off when you are not there, and yes, I would let the BO know that she is making it worse and you are afraid someone will get hurt. Just the facts, ma'am.