Respectfully, this is not my belief when it comes to obesity, particularly for super fat people. Most people, I’d argue, have some kind of pain / trauma that they are using food to self soothe with, rather than other substances e.g drugs / alcohol.I get the feeling it's not the parents in charge or control in that household ..those two toddler adults rule the roost !
Please don't come at me, this is just a thought....
Could that be because she doesn't have any issues apart from the fact she loves food ? She was a spoilt overfed child that has grown into a spoilt adult that loves food ? Her and the brother clearly have no concept of portion size and are both privileged in that they are used to eat rich calorific foods as and when they fancy. I still can't get past the size of the roast dinners they both used to consume in one sitting and the amount they eat generally.
I’m not qualified in this area however I do have family experience with addiction (drugs / alcohol / gambling!) so my opinion comes from that. Food addiction and eating disorders are real and therapy could really help someone like her.