My Hannah is about the same age is your little girl. I dish her a small amount of everything on offer and if she finishes it all, she can ask for seconds of any particular one (or more). For example, I might dish her chicken, potato and peas in the first lot but once that is finished she has her choice of whatever is left. She might say that she wants chicken and potato but not peas.
The other thing to watch is when her last snack is before dinner time. We have lunch about 12, afternoon tea about 3 and dinner about 5.30. I will only give her more to eat between 3 and 5.30 on exception, say if we are out, tea is going to be late, or if she's not well. If she says she's hungry at 5pm I say, that's good, we need to let your tummy get hungry for dinner
I think the other thing is that if all your meals are generally nutritious, you don't seem to worry too much if they are picky eaters at the odd meal time.
Hope there's something helpful in all that.