Yanbu but as this thread shows, it’s a very sensitive issue. Both of my step daughters have weight issues, one finds it easier to manage than the other, and stays at the top end of overweight. The other is morbidly obese.
It is devastating for their father, who tries so hard to model good behaviour, fitness and healthy eating, but their eating patterns were set in childhood by their mother, who herself was a yo yo dieter.
Unfortunately when they do lose weight, it’s always from a quick fix, and never sustained. I also suspect the partner of the morbidly obese daughter is a feeder, as she has put on even more weight since they got together, despite the partner keeping himself fit.
For some reason society doesn’t like us talking about obesity and we are not allowed to express concern in the same way we could if someone was drinking or snorting themselves to an early grave. You have every right to be concerned about your daughter, just as OH has every right to be concerned about his daughter. The one true thing is that the fix for the issue has to come from your daughter. Getting fit and healthy takes time and effort, and once you get there it still needs time and effort. Society makes it much easier to give up and make excuses, and starts the spiral into self loathing.
I hope your daughter learns to love herself enough to realise she and her body are worth taking care of. Good luck.