Am so sorry, I am having a bit of a cry for you, it's just awful what you've been through and what this bitch has done. I really want you to know that not all people are like this, and you need support and caring and some human empathy. What you've had is a big fucking slap in the face, betrayal and cruelty. You don't deserve this or anything that's happened to you.
Don't leave, try and tell some of the other nannies what happened, and just wait and see how they react - I suspect they might surprise you.
I agree with others that you might want to give councelling a go, you have had so much happen to you, and it's a huge load for you to bear and try and process on your own. It may help you.
One thing I learnt when I had some councelling, I'll tell you and you can ignore of its not a helpful thing! He explained it alot better than
I will..,
Your life is made up of all the tiny interactions that happen everyday, if the majority are negative, even just tiny tiny things, then how can you stand against it all day, it will end up weighing on you and you can't resist it all day after day, it's too much for anyone. So if you start trying to care for yourself by minimising the bad interactions, even the tiny ones, and treasuring the good ones, it goes a long way to helping you get to a better place.
May not help you at all, but at the time I was surrounded by abusive or unkind people, and I'd lost sight of the fact that I deserved better, everyone deserves better. I had stopped making an effort to protect myself against people, or to gravitate towards better interactions. So I started counting the good interactions, and tried to move towards them, & make an active decision to move away from the bad ones. It was actually work people that got me down the most, cos I was so busy trying to protect myself from abusive h, nasty family etc, that somehow I thought the low level stuff wasn't worth caring about, but actually had a huge effect and made me feel surrounded by unkindness and cruelty. I assumed the whole world was like that.
Anyway, may not help but just in case xxx