This 4 year old has control over you. But, good news is, you CAN turn this around.
First, do not ever let her wining or fit throwing be effective. If she wants something, she needs to use her big girl voice and ask like a big girl. Give her an example "Mommy, may I please have a peanut butter and jelly sandwich?" That should be the only way she will get it. "Your response could be, "Yes you may. Thank you for asking so nicely."
Be firm with her (but not yelling) and tell her you cannot hear her when she whines. Giving her what she wants, even one time, tells her that her wining and fits are effective.
Make sure you model the behavior you want her to have and use your manners as well. If she hears you wining and yelling, she will do the same. Keep your calm, (even if it means walking away for a moment) and use your manners too. Remember to speak FIRMLY, but respectfully.
When she does throw herself on the floor, walk away. Do not give this behavior any attention. When she has calmed down, get down to her eye level, look her straight in the eye, speak calmly but FIRMLY, not yelling, and say "Your behavior is not ok. It is unacceptable. When you are angry, you use your big girl words." Give her a chance to use kind words to talk to you, then the situation is over.
You have to be consistent at all times with this. Giving in even one time can be a huge set back and give her mixed messages.
Giving her more choices throughout the day when she has good behavior can also help. And act cheerful when you ask "Would you like cereal, toast, or eggs for breakfast? Orange juice or milk?" "Would you like to go on a walk or to the park?" "Do you want to wear your blue pants or the red one's?" In the case that she throws a fit and says neither, DO NOT give in. Either she wears the red or blue pants, or she goes in her pajama's. If she screams about not wanting toast OR cereal, then she can eat later when she decides which one she wants. If you are leaving and she can't eat later, bring it with you for later. The moment she begins to whine, tell her you will listen when she is ready to use big girl words, and walk away. She can come to you when she is ready.
Bottom line, YOU have to be in control and SHOW her that you are serious. Kids need limits, although they don't know it. Limits hep them feel safe and secure. Model what good behavior looks like. Try to be silly with her and have fun. Take some of the attention off her fits and have fun, regardless of her behavior. Show her that her screaming and fits have no effect on you.
I work with young children and families. PLEASE let me know if you would like to talk further about this. You CAN get a handle on this and it is important that this happens now, before she gets much older.
Best wishes, C.