Just wanted to say Joey good on you for doing something though and being concerned. I think my parents pushed the "we love you no matter what shape you are" a bit too much and not enough of the "we love you so we want you to be healthy". So it's great to be doing something and I think about making it about a healthy lifestyle (and not neccessarily results) is a great approach. But you do need to talk to her Dad. You can make a healthy environment at your place, but that needs to be mirrored at her Dad's too.
Thank you also very much for your reply. I think that she doesn't really get noticed too much as over weight or teased (thank goodness) because there are so many children that are overweight, she kind of just fits in. Which is good for her socially. I just really struggle because I am and have always been very sporty and also very conscious of my weight.