R.C.
I agree--she is officially three years old!
Not taking it seriously is crucial. I do a lot better now with my son (second child!) than I did with my daughter, so I can say that laughing helps. Keep firm boundaries, but doing the unexpected helps a lot. I can take my son to bed laughing if I carry him by the ankles, but he'd throw a whole huge tantrum if I tried to do it normally. He still gets to bed on time.
Other tricks--let them "do it themselves" as much as possible. Give them "either or" choices if you really don't care. Both of these help with food. Do you want goldfish or pretzels? Okay, you can help me pour them in the bowl.
And try non-breakfast food in the morning. If she eats sandwiches, that's breakfast! I think breakfast is important, but they won't starve themselves. Just hold firm on the snacks.
Anytime you can use distraction or redirection to avoid a battle of wills, I would. Not bribery, but if you know they don't like to sit down to eat, see if you can get them to carry something to the table and sit before they realize that they meant to fight you!
Good luck! They do outgrow it :-)