This girl probably weighs as much as Lena Dunham, but Lena Dunham is fat because her stomach sticks out further than her tits.
I see women all the time who look like they're maybe 160-180 lbs (depending on height), but if they have small waists, big boobs, big thighs and asses. I oddly don't consider them fat and don't mind the extra weight. I basically think its all about the bust-waist-hip ratio.
Then I see girls who are 135 pounds but have narrow hips, no breasts and a slight gut and I think they're whales. That is the most hideous body type to me. Girls who have boyish figures and no waists have to stay Natalie Portman skinny for me to like them or they start getting "chunky"
Kate Upton (except her tits) is a good example of what happens when skinny girls with no figures gain weight. We've all seen the terrible pudgy ass and fridge torso.