Honey said herself that she was a teenager who hated her body. They were trying to help her hate her body less. And I'm sure they didn't tell her to aim for 9 stone. I cannot imagine jane (from what little I know about her) thinking that a woman has to be thin to have a good sense of herself.
Describing her parents approach as toxic (which I think she was basically doing) is a bit harsh. They didn't want to stand back and do nothing when she was unhappy and hated her body.