Wow, was my first reaction to your post. It's hard to tell who is the parent. Obviously, you have spoiled your daughter immensely and she knows how to manipulate you to get what she wants. You need to go out today and by the book "Boundaries" by Dr. Henry Cloud, you need to read it ASAP. It may even be at your local library. Remember you are the parent. As a rule, I never give in to ultimatums, it immediately gives the other person power over you, and lays the foundation for them to manipulate you in the future. I don't know how she made your life hell before, but she could only do what you allowed and accepted.