We had the same problems with our first helper, she was hired with the recommendation of my friend's friend, when we were urgently looking for one. After 1.5 years miserable time she gave us, we decided to stopped the pain. I was a lot more careful choosing the second one, she was very good, kids loved her. Unfortunately, she had to go back after a 2-year contract. Our new one is good at cleaning, cooking, and house chores, but doesnt have much idea of babysitting(we have a 4.5 years old boy and a nearly 3 girl), but still way better than the first one.
Get rid of her and get a new one, if you choose carefully and maybe have one-day try out with cleaner hourly rate, it can't be worse than your current one