I would be pissed off too OP.
How rude of her...Even if she felt short-changed, for her to verbally tell you is just horrible of her. I would never come out and tell anyone that.
I am sorry for what she did to you, your family did not deserve it at all and know in your heart that you did the right thing, since she left you...You owed her zilch. Nada. Not a dime.
People like her, so ungrateful will get theirs someday. Trust me. Karma.
I hope you find a great nanny soon. Any nanny would be blessed to work for such generous people like you.
Good riddance to the last one.