My 9-year old is the perfect weight but she has a tummy too. She eats healthy food, we allow sweets in moderation and she does 5 hours a week or more of cheerleading/dance/gymnastics. We're not worried because we're pretty sure her tummy is leftover "baby fat" and will go away in its own time.
That being said, she gets self-conscious about it sometimes. When she does I let her know that everyone has something they don't like about their body or wish they could change so she's not alone. We should worry about the things we CAN change, like who we are.
I know that sounds all cheesy but it seems to work for her. We also talk to her about why she likes her friends. Does she like them because they are tall, short, have blonde hair or are skinny? NO! She like them because of who they are.
One thing we DO help her with is to dress in a way that's flattering to her. Every girl likes to feel beautiful, and the right clothing can do that. My daughter really wanted a bikini, and while I don't really love the fact that little girls are wearing bikinis, I let her try on a few. The top of the bikini bottoms hit right under her belly and the top hit right on top of it. She LOOKED like she had an even bigger belly, and that's when she commented on it in the dressing room. So I encouraged her to try on some tankinis so she could still have the two-piece option. She LOVED how she looked! It's now her favorite suit and I think she looks absolutely darling in it.
Try taking your daughter shopping and try on lots of different clothes in different styles. Make it a fun day with lots of modeling! Help her to discover which clothes make her feel pretty. From watching a lot of those makeover shows, sometimes changing the outside CAN help you feel prettier on the inside. It's not a bad thing.
Your daughter is beautiful just the way she is! I hope you can help her to see that.