Hi D.,
Funny you should mention such a topic, I have a similar issue with my 4 yr old son. Many a night he goes without dinner by his choosing. He is very picky. I simply refuse to make him a separate meal each night though just because he doesn't want what I made. I put very reasonable things on his plate. I don't get upset, but I let him know that the kitchen closes at 7:30pm for dinner, and no one gets dessert after 8pm.
I tell him that if he'd like to go without dinner that is his choice, but he will be very hungry. He also eats a great breakfast and lunch. I sneak as much healthy stuff into those other meals as possible and he takes a multivitamin.
If you don't have bed wetting issues I'd say keep a cup of water available up until bedtime, offer dinner at your normal dinner hour, and let her make up her mind. Ask her pediatrician, and if you are really concerned about weight, just weigh her twice a month to be sure. Watch out for under eye circles as that can indicate iron loss.
Good job Mom, just keep doing your best!