You do whatever you feel you need to do. You asked for opinions and this is an area I am experienced in my country.

I am truely sorry you have been hurt by them but making a case against them is not going to benefit you or them in any way. If anything it will put them off hiring mentally ill people. They do not have to, nor do they have to supply services to anyone they do not want to. This may be "against the law" but barns rarely run to the book.

If he horse world is anything like here, this is going to go badly for you and your reputation. Especially if you want to work in other barns, or board your horse. Be aware of what could happen for you if you choose to go through with this. And live with the consequences of your actions.