This was me. I was never slim, but I was sporty. WhenI was in my early teens I began putting on weight, and we aren't just talking puppy fat, I think I ended up putting on 3 or 4 stone after about 3 years. I had absolutely no idea, how could that be? How could I have no idea? Well, I had never been one of those willowy kids, I'd always been bigger, and I was doing exactly what my friends were doing in terms of eating and exercise. They weren't putting on weight, so why would I think I was? I changed the style of clothes I wore so I didn't notice them getting tight.
I know this is a zombie thread but I wanted to say something, as this thread really touched me. To this day I would say that I haven't really recovered from the moment that I realised. I have never been so humiliated in my life, as when I realised that EVERYONE knew except me, had seen me inflate and continue to keep eating, even my parents has spoken about it behind my back, my parents who i loved and trusted more than anyone else. I felt so betrayed. I was suddenly saw what everyone else saw and was repulsed by myself, I believed no one would ever find me attractive ever. My self esteem was suddenly just gone. Then, the trying to shift such a lot of weight when your friends can eat or drink what they like "why are you having salad? You hate salad" and thn seeing their faces when they realise that you finally know... It took me at least twenty years to undo the damage to my confidence, and if I'm honest my insecurities still linger.
I suppose my point is this, if she's a little chubby, not too overweight, subtly encourage her and lead by example as PPs have suggested. But if she is actually getting unhealthily overweight, you need to speak to her. Do you think she is actively choosing to be fat and eat rubbish over being slim and healthy? My parents did. As a parent the first thing your job is is to keep her healthy. I found it very, very difficult to forgive my own parents lack of action when it was me who had to cut out food and spend hours at the gym to undo what I had unknowingly done to myself. I know I am projecting massively, but please don't let what happened to me happen to your daughter.