M.S.
Denise,
I suggest going about it in a very different way. You could speak to her and tell her that you have decided that you want your child to eat healthy and adopt a healthy lifestyle and that you are contacting all your daughters friends and parents for help. You can then ask her for help in implementing it- and maybe see if her daughter wants to join your daughter in healthy eating or exercising- (join ballet/ride bikes etc). I know that you said that you eat healthy and monitor your child's eating-but its just a non-confrontational way of getting a suggestion in to someone who may not hear it otherwise. If you make it sound like you need help with it-she may be more open to bringing her child in on it too-at the very least,she would see continuous positive changes in your child and learn more about healthy food and lifestyle.
Good luck!
Molly