16 year olds are bloody hard work.
However, you are being so accomodating that your DD will never value anything you do. SHe walks all over you and you still come back for more. SO on your birthday meal, you will not only be missing a person, but will also have to fetch her at 2am - so no drinkies for you, no relaing evening, no snuggles with DH, becausse one of you is going to have to fetch madam at 2am....nice birthday.
My opinion, as a mother of a 16yo DD....
Let her go to the ball on the proviso that she is home by 2 and she needs to arrange her own lift home. No lift, no ball. If she doesnt like it, tough.
If she wants to live at the boyfriend, let her. However, speak to the BFs mum and ask if that has been discussed and let her know whats going on at home, so that the BF family have a choice about whether or not they can accept that. Get them on side, as ultimately, teenage relationships are a transient. Plus they must be at college - theres a lot of work to be done, and they need to focus.
Id also make it clear to DD that if she chooses to move out, you will not provide any financial assistance. ANd that the BF family will expect £25-30 a week board - make sure she knows that food, water, electricity etc do not come cheap. Tough love it out.
Washing: In our house, if its not in the basket on washing day, it doesnt get done by me. My DD currently has most of her stuff on the floordrobe. SHe has no clean knickers. I dont care, as until they are in the laundry basket, they are not my responsibility.
Food: In our house, there is always food on the table at a set time, If she eats it, good, if shes not there and has not let me know she is not requiring dinner then my gannet ds will eat her share. There is food in the fridge and she can make herself something.
Clothes: SHe earns £150pm and you are still buying her clothes? That stops today! Let her buy her own clothing, her own specialist toiletries. Obviously you can provide soap, toothpaste and whatever family shampoo/showergel is required, but she should buy the rest.
I think a basic phone contract (capped - I use Tesco) is something I would (and do) continue to provide.
You need to let her know that this entitled behaviour has consequences, and that you are queen in your home, not her.
You will not lose her through being tough. She may hate you for a while, but she will come back eventually and appreciate what a cow she was.