I think you're putting the cart before the horse. They end up lonely and secluded because of their emotional rëtardation.
Deathfats are created by a childhood environment wherein they're either rewarded or placated with food, all the time. They come to use food as an all-purpose stress relief, and those of them who fail to mature emotionally (which can be partially sabotaged by obesity's effects on confidence) end up as deathfats. They're legal adults, but mentally they're just huge children who simultaneously avoid as much responsibility as possible and ingest huge amounts of food to "cope" with anxiety. Then, since they alienate everybody because they're huge toddlers, they become isolated, and isolation in this day and age means living solely through the internet, to the degradation of real-life social skills. This isolation leads to delusional thinking exacerbated by depression and anxiety; in males it often creates the NEET incel nutjob stereotype, and in Chantal we see its apparent effect on females.
Here we arrive at Chantal proper. She's been allowed by enabling family and a socialist welfare state to age to 35 without ever having become an adult, and now resides in a dim, musty world of massive food consumption and obsessive preoccupation with trivial online interactions. She doesn't have a real life to think about, so she grossly inflates the importance of ludicrously unimportant things like YouTube comments. Like bourgeois SJW teenagers, she needs an imaginary struggle, to define herself: as Freud asserted, identity is conflict.
Is Chantal therefore a mere victim of circumstance? No. Her nutjob mother did a shitty job of raising her, but if everyone who grew up with subpar parenting was as useless as Chantal, society would be in ruins. It's her own sloth and gluttony, either of which are overcome by maturity and willpower, that have rended her a foul-smelling social untouchable. She may refuse to behave like an adult, but she is one, and like all us adults she has to live with her own decisions - no matter how selfish and sybaritic.