Please tell me there’s an end in sight, and that this phase - like the twos - will pass.
[name]Hi[/name] - I have a four year old. Although I don’t know what frustrations you are dealing with, I can say my daughter is clearly more aware of her independence and power to affect people. (her favorite thing to say is “I am not giving up!”). She is experimenting with asserting herself. She thinks in a black and white manner and the perspectives of others are frequently lost on her. This combination of attributes and skills is completely age appropriate and quite frustrating to deal with at times. I get so irritated with her obstinance. I frequently have to remind myself that she has to go through this to develop as a social being and it is my job to guide her by appreciating her growth, instructing her about where boundaries lie and redirecting her when she crosses them. We have lots of time outs and I try very hard to deliver them calmly and firmly. Her parents are in charge and we respect her emmensly but have to be responsible for her behavior.
I don’t have a 4 year old of my own, but chiming in since I’ve taught a 4 year old ballet class for several years now…
Like lynae said, there’s so much experimenting with pushing limits. I find that my 4s are much more focused on fairness (“Thats not fair!”) than any other age group, everything matters soooo much and friends groups are starting to emerge causing all kinds of issues. With many 4s, especially the girls, you can really talk through things, ask questions and encourage them to explain their words and actions. Sometimes I’ll get to the root of an issue in class this way and they really do appreciate it when adults expect a lot from them and hold them accountable.
They mirror their parents so much, so modeling good behaviors makes a world of difference. The way they see mom talking to them is often the way they will talk to others (with sometimes disastrous results).
I phrase nothing in the form of a question unless it’s truly an option. When something is a statement, it’s a statement. “We’re going to do this” not “[name]How[/name] about we do this?” It’s amazing how much wording matters and I’m sure you’ve found that out.
This too shall pass, by the time they arrive in the 5-7 yr old group, life is a lot easier!
But of course, I get to send them back home with you after an hour!!! (hahaha 
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I agree with wverything lineska said - especially the above.
I now have a 6yr old, 2yr old & 6wk old. I’ve come to the conclusion that the first year is the easiest & it just gets harder from there. By the time you got one thing figured out & how to handle it, they throw you a curve ball & BANG! Whole new ballgame! The challenges just keep evolving & changing as they age until one day they become adults & have to answer to themselves.
That’s my 2 cents. So find joy in that 4yrs old is easier than 14yrs old. 
This is the problem that we have at our house, and it’s been going on since he was about 3 1/2. And got much worse after he had his tonsils out, though his doctor swears the bi-polar mood swings will pass in a few months.
I’m a “Statement” Mom who is married to a “Question” Dad.
Me: “W, it’s time to take a bath. Let’s go.”
Dad: “W, Are you ready to take a bath?”
Everything is a question with my husband, and it’s awful. My son knows that he’s in charge when Dad’s around. And I’m “mean.” Always… “You’re mean, Mommy.” “I don’t like you, Mommy.” On and on.
4 is so frustrating.