Skipping lightly over the delicate issue of slating the physical characteristics of a morbidly obese woman on a weight loss forum, which frankly is stepping onto ground I think is inappropriate, it seems as though she has been encouraged by the attention she has been getting because of her weight into pushing the boundaries in order to make a name/living for herself based on her weight. Which is clearly where she now sees her value in life as lying, not as a responsible mother or a healthy example to her kids, and that's a shame.
There is a market for this in adult "entertainment" although it could be argued that watching a woman knowingly choose to shorten and take risks with her life is far from entertaining, that market will always exist, just as the appetite for exceptionally skinny and waif like women will exist. I don't believe people willingly choose what sort of body shape turns them on any more than I believe that you can choose your sexuality, or that paedophiles choose to have sexual feelings toward children.
What is a choice is whether or not the person chooses to facilitate and perpetuate those feelings by engaging in activities whereby they encounter the object of their feelings, and that's very different to simply having and acknowledging them to yourself. No-one ever got hurt by an unvoiced or unacted upon thought.
But people do act upon those feelings and that is why markets like this will always exist, whatever the wider society may think of them. She is choosing to eat the way she does with wilful intent, which she has every right to do, but the victims in her pursuit of that intent will be the children she bore that never asked for a mother who ate herself to death to prove a point. And while I don't wish her dead, their lives will most likely in many aspects be improved when her body eventually does give up under the strain.