Oh man, they can drive you a little bonkers, can't they? This would definitely test my patience. I'm guessing she is your only child?
So, what I'd do in all sincerity with new earnestness is to tell her the new rule. She may ask for something once and has one chance to receive what she has asked for. Just one. And at that point, if she refuses, she will not get another opportunity. Explain it to her. Then do not bend. Do not indulge. If my child asked for water I would not worry about what cup, what faucet, etc. If I did it wrong, that is okay, she has her one chance to drink it or that is it. She will not thirst to death at night without the drink of water. :>)) So, one shot and then whether she has a fit or not, that's it. Ignore all fits. PRAISE all good behavior. No matter how small. Positive attention can be something some kiddos crave. You can try something like a positive bean jar so when she does it the first time, you put a bean in the jar. She gets 1o beans or whatever it is and gets a treat like picking which game to play, which park to go to, getting an ice cream, etc. (small treat and nothing like a toy). If she doesn't do it the first time, a bean is removed, just one.
What is up with the waking up and waking you up 4 times a night? I'd nip that in the bud as well which I know can be hard but it's time. For a drink of water--- we put a sippy cup by our kids. Filled it every night before bed. To this day, they put water by their bed at night (themselves) and they are teenagers. In no way should you have to be getting up 4 times a night and putting her back to bed. If she is sick? Yes, get up. But at 4, that's not necessary. Tell her we all need good sleep. YOU and her both. And she needs to stay in her bed. She may go potty and get back into bed. And this is hard but if she comes into your room, you can either walk her to her bed silently with no ritual or cuddles or sweetness, just walk and put in bed and walk out or you can tell her you can't get up and she should go get in her bed. She can handle that! I promise.
My younger son was (still is) very sweet. But since he was tiny, he tried to control where everyone sits. At the table, in our family room, in the car, if we go to a restaurant or a movie theatre. And it doesn't always work out his way. He wants to never sit on the end, wants to sit next to me, blah blah blah. And I have another child who also wants to sit by me. Taking turns when it was just the three of us was not an option! Fits would ensue. For a long time I thought it was easier to just do it his way. But after he threw a fit in a friend of mine's car when transporting several kids because he had to sit in a specific spot and it wasn't working, I was like DONE. Then I just ignored it. He still wants things in a certain order when we sit. But he's older now. lol. He's a teen so we just laugh about it and move on. That was definitely his hot button.
Parenting is very tiring! Does she do great behaviorally in school and is the obstinance just with you? Moms usually get to see the good, the bad and the ugly that all kids have. :>) Hang in there.
How is it going with your little cherub? :>))