I used to have the opposite problem. I was always the "fatty" when I was younger. Not very overweight, just maybe 20-25 pounds, but not like all the other fit and thin women that were of my acquaintance. My advantage was that I cycled a lot ever since I was 16 tears old. They couldn't understand why they couldn't keep up with me (the fatty) on social rides. They even tried my bike to see if it made a difference. It didn't. I think you have lots of info from smart people, but I just had to say something from being on the other side.
