This sounds like an incredibly unfortunate situation to be in. When you say that the university "refuses to find another supervisor", are they being serious that there is nobody else who can replace her? Or is it that they simply do not want to help you look for another one?
When I was about 20 months into my research, I requested a new supervisor on the grounds of conduct unbecoming of a PhD supervisor (ie. he was bullying me and deliberately excluding me from opportunities given to his other PhD students, among other things) and after I showed him evidence to support my claims the wheels were immediately put in motion to have him removed from my panel and find a new supervisor.
My new supervisor is a massive improvement over my old one, although I have a sneaking suspicion that my former supervisor continues to blacklist me to people in the same area of research to me. But there are ways around him. You may need to find side doors around this monster, I can't believe that she is the be all and end all. Nobody is.

I agree. I think the university are calling your bluff, or whatever the correct expression is here. They think that you either don't know your rights or will not assert them (i.e., by saying that you must have a new supervisor in order to continue).

Calling the bluff is the correct expression. :)
I find it impossible to believe that with sufficient written evidence to support your claim that the university cannot enable you to find a new supervisor. Like all educational institutions, they must have an anti-bullying policy, and this woman is abusing her position of power.
Universities should not grant senior academics too much autonomy, because this paves the way for abuses of power to pass unchecked. There must be greater accountability for PhD supervisors who misbehave and for the institution itself to provide a safe environment for studying.