Doreon,
I think this is a VERY common power struggle that I have gone through and seen both my SILs go through with their kids.
For us, when you get up, you're done. Now after that there's a choice. IF they really never ate much, I cover the plate and put it in the fridge. Then when someone says they are hungry the ONLY choice is "lunch all over again". This prevents them from eating snacks all the time or choosing what foods they will eat. For me, it prevents wasting food and remaking meals. The second option, if they did kind of eat well, just not as much as I think they should have, then the next "snack" option is only healthy food - apple slices, banana, crackers and cheese, etc. NO cookies, fruit snacks or "food auction" (where they tell me what they are going to eat).
I too never wanted to make food a point of contention. But I also realize that we cannot graze all day long, allow small children to tell us what they are or aren't going to eat, continuously waste good food or let them wander during mealtime. The reality is that she is moving out of "baby phase" when we are kind of told to feed them on demand, to "toddler phase" where even preschools have "meal times" and "snack times".
I have seen too many kids who control their parents by making food an issue. Let's face it, many Americans are overweight. Are kids are most likely NOT starving. Although she may be eating less than you like, I say, when she gets up, the meal is OVER. Try this for a week or so (be prepared for sobs and her being upset), but she'll "get it". I can't believe how many 5 year olds I hear that will ONLY eat chicken nuggets, PB&J, or McDonalds. Let's be real. WE are the parents.
Be a role model for healthy eating and "house rules" as to what is acceptable behavior. Make sure YOU don't turn food into a fight. Taking away her plate after she leaves the table IS NOT a punishment, it's HER CHOICE. If she says 10 mins later "I'm hungry", give her ice water and tell her she needs to wait until snack time, dinner time, whatever is next. Tell her SHE DECIDED to leave the table and when her lunch was over. Don't let her wander with food. The kitchen table is where food is served. I'd kind of stick with the same "rules" for your baby too. Sit in the kitchen when you feed him, unless it's a bottle. If she asks why the rule is different, tell her that he's still a baby and when he eats big people food, it IS at the kitchen table.
I sincerely believe this is an innocent, but very real struggle many of us go through. Decide how to handle it and stick to your guns. YOU are the parent. Don't let whining manipulate you or your decisions.
I hope this is helpful without sounding like I'm on a soapbox. I really think that at 4 it is very reasonable to expect her to ONLY eat meals at the kitchen table.
Good luck!
Sara