Robbo must have genuinely disordered eating and body image. Part of me believes that the minute she gains 1 or 2 lbs she begins to see herself as the "fat girl" again, which is why she preaches about body positivity. She wants to make herself feel better. I think she has the "fat girl" mentality, she spent so many years being big and now even though she has lost weight, she still sees herself as that person (especially since she gained some weight from her smallest).
Even when she dresses in revealing clothes she does not look comfortable and you could never imagine her wearing those clothes out. She doesn't seem to see herself as this girl who does have an enviable body (and she does have an enviable body to some - she isn't defined or ripped but she has a nice hourglass figure, barely noticeable stretch marks and she has managed to maintain an impressive weight loss).
And I am speaking as someone who was big, then smaller and now bigger again.