She didn't just lose 100 lbs - that skin is fairly taut. You lose 100 lbs, you sag like hell, even at her age.
And she didn't just run a marathon. With such a load on her weight-bearing joints, I doubt that she could walk a marathon without serious pain.
Yes it's mean to pick on fat people, but making up a positive back story doesn't make fat healthy. Yes, skinny people get diabetes; part of it is genetic, but I have also seen (not read about, or heard about) patients normalize their blood sugar by losing weight. They didn't get to model-thin, either, just down to a normal BMI. And excess weight will tear the hell out of your feet, ankles, knees, and hips - yes, skinny people get arthritis, too, but being obese will cause more damage sooner - and will make repairs more likely to fail. It's not a judgement, it's simple mechanics.