So, look for another job, get hired, and give her 2 or 4 weeks of notice.
Done.
Some people will never value you. Others will. Find someone who will. She sounds like a horrible person, because believe me, IF you had a child she'd still expect you to do all those things "because you are the nanny and I want this."
So find another job, and leave. Do it right, but leave. There are so many wonderful families looking for the right nanny, find that family and be gone!