What should I do when a professor is teaching inaccurately?
Your professor sounds simply incompetent - sorry you have to deal with this, but it is an unfortunate fact of life that one runs across such people every once in a while, in academia and pretty much everywhere else.
As for what to do: about the unfair grading, follow the process for appealing a grade. About her general incompetence, if she is grossly incompetent, a reasonable option would be to complain about her to the art history department. If she is only mildly incompetent, you can drop the class or leave a bad review at the end of the semester. Those are your options really, I doubt anyone will be able to offer anything substantially different. Good luck!