I have a DCG like this too. She can eat more than my 8 year old.

I sometimes worry about whether I am overfeeding her but if she insists then usually I will give her more. Her parents are aware she eats a lot and aren't worried. I wouldn't want to make it a big deal for the girl or her parents.

Other times I will cut her off after seconds or thirds and invite her to come play or take her to wash hands (which she loves doing) and see if she moves on to the next activity. I usually draw the line at thirds with all the children.

Some other kids I have can eat normally but then go through a growth spurt and suddenly eat a horse. Maybe your dcg is just going through a growth phase?