Very late reply here, but

Sandy's sister was starting from the place Yvain's article left off - having dissolved the kind of shallow disagreement between the men, she had probably moved into her personal toolbox for actually helping her sister process an emotionally complex situation that was likely to pose serious problems in finding and executing the right strategy in the face of hostile epistemic influences and possible akrasia if she started feeling really guilty for enjoying food and carrying a few extra pounds. Politicizing the issues and "blaming society" isn't without costs or failure modes, but it can help with some people get out of "guilt mode" and start using their brain.

Note that Sandy's sister started with a examination of the personal choices available to Sandy, the information sources available to her, and the incentives and goals of the people offering the various theories. I assume that after Sandy got into an emotionally safe context to talk about her issues, there's a chance she would decide to do something in her power to change course and decrease her weight.

It is not my experience that people who support obesity as a valid life choice and decry "fat-ism" as akin to sexism and racism tend to take this next step.