I think it depends on the wastage? If it's marginal I wouldn't worry. If it's twice her actual consumption I would monitor it.

Could it be related to her wanting to be a grown up? Situations like this are an opportunity to learn. And don't have to be a power struggle. Talk to her about food wastage, and not to be cliche, but about those that don't have food, the value of food and look at pictures of the varying sizes of stomachs. Explain she can't physically eat as much as she dishes out. I wouldn't suggest serving her food again as this has been proven to lead to psychological problems with food ie. finish what's on my plate or I'll eat it cold later which leads to overeating and being part of the clean plate club.

We encourage our children to eat to full even if it means leaving stuff on their plate. And if they really enjoyed it and don't want to waste it, then most things can be saved for later (but it's not enforced). I have a fear of an unhealthy relationship with food because I had one and I'm still fighting against it. But at the same time I think you can work through this without it being a huge drama. Just try not to focus on finishing what she has prepared for herself. And maybe remind her that being little is just as awesome as being a grown up. It sounds like she sees this as being inferior. And I think that's the issue, more than the food.