Karen was always one of the pretty girls at school. The ones who got with the jocks, lost her virginity at the age of fifteen, and then never looked back. She was almost so popular, that it went to her head. She became image-obsessed, and not soon after her GCSEs started, she became anorexic. She battled with herself to lose more and more weight, to keep up with the models and the divas of the fashion world. It was what she lusted after. 

When she eventually became pregnant with Erica at twenty, her body suffered, and she was forced to gain the weight, otherwise, it would have had adverse effects of Erica’s health. After she'd given birth to Erica and Felicity, she gained loads of weight. And since Rupert has been wealthy, she's been able to afford a personal trainer and a psychologist to keep her on track, to make sure she doesn't damage herself again. 
Nobody knows why or where her desire to lose drastic amounts of weight came from. It wasn't anything at home. She had a nice childhood. And her parents and brother loved her very much, even though she doesn't keep in contact with them now.

A few years ago, they all had a family disagreement about Rupert and his line of work. They didn't like who he was defending, and how he was making his money. But Karen stuck by him and defended him. Said that he was just doing his job, and doing it well. Said that there was nothing illegal about what he was doing.