Oh I wouldn't be worried about a podgy belly!! I find them cute!!

My DD has been best friends with a girl since they were 2 at pre school who is a little podgy but only in her belly and she always has been, and she is more active than my DD (plays multiple sports, as well as swimming and playing) and eats really well, and her mum and sister are tall and thin.. It's just her body shape! She just has a little belly!

At the age her current body shape is not really an indicator of what it will be in the future, and I know you want to guide her in the right direction and I think that's great, just stress the importance of good food and drinking lots of water and playing sport and she will be fine