I had a similar problem where I board. Owner never worked with horse and horse put me and my horses in danger almost constantly. You did the right thing. I have a system in place for other peoples horses: 1. Talk to BO/BM, report problem and look for improvments. 2. Calmly talk to owner and let them know of your concerns. 3. Don't take any crap from their horse and do what you have to do to protect yourself.
It's ridiculous for any owner to do as she is doing and allow a horse to be dangerous. Good luck and I'm rooting for you :)