I've just moved back to live in my childhood home after 30 years and found some of my favourite teenage clothes stashed away in a trunk.
At 17 I was 5'10", weighed 11 stone 4lb and regarded myself as a monstrously large freak because apart from being 6" taller than most of my friends, (the average height for a woman back then was 5'4") I wore size 14 clothes.
A Wallis skirt from 1978 labelled size 14 which I discovered in the trunk looked so tiny that I measured it out of curiousity and discovered the waist was exactly 26" and the hips 38".
In the mid-1970s, size 10 vital statistics were 32",22",34", 12 was 34",24" 36, and 14 was 36", 26", 38" etc. It was virtually impossible to find clothes larger than size 16 in High Street shops, and there was a very limited range in size 16.
Women are definately taller and heavier than a generation ago. I used to shop in specialist "tall girl" shops, but can buy clothes anywhere now. And guess what? I'm still a size 14, even though I'm two stone heavier than in my teens!
BTW, that lass in the OP hasn't got a fat belly IMO - looks like loose skin after losing a lot of weight too quickly.