Went through a similar situation. I'm a believer in prayer. So I prayed. Within the first year she quit for a better job and we were back to a much healthier work environment.

Just do your job. If she steps in and takes over some things and you're questioned about them, just say you were fine with doing them and would like to still, but she decided she wanted to do them and didn't ask your input so they need to ask her about those things she's now taken over. Offer to take on some additional duties to keep busy. She can only take on so much, and if you don't quit, she'll eventually burn out or give up and find another job where she can pull that on someone else. If the office is in chaos and wasn't before, people will start looking for the cause and realize when it started.