I was overweight like your daughter at 8 and I knew about it because of the way that others reacted to me. My mum refused to buy me clothes I liked (I remember clearly wanting this spice girls top and she said no you look too fat in it) there were snide comments at school and knowing looks between adults. Your daughter will allready know what people think. so my thought would be it’s pointless not acknowledging her.
however, with hindsight what I really wanted when I was little was for my mum to help me take control of my weight. I had no clue why I was fatter than others, since I only ate what I was given. I used to steal food from the fridge sometimes (I had a sad childhood) but I never really joined the dots on how that affected my weight.
I think if my mum had maybe acknowledged the issue, like others have said, as a health issue, and then completely taken control of the diet (menu, portion size, availability of snacks) and had just done it without further comments it would have sorted the weight without the years of hurtful comments and interventions from other family members who seemed to think being an overweight child was my fault and my responsibility to change.
I would try to address the diet and keep discussion of her appearance to a minimum, I would try not to get drawn into details, just explain that this is the food we are having and it will be really good for us and we will all feel better soon.
as a side note and I don’t know if helpful, when I was 8 I would see food as a massive treat and think about eating all the time, and I think that it was because I needed the comfort. there were lots of issues at home and I never had any channel for my interests etc, is your daughter going through any unhappiness of her own? If so could anything be done to improve her mood / give her an outlet besides food?
good luck with it x