Amber's not constantly feeding us crazy bullshit stories that sound straight from a sitcom like a pathological liar would, she mostly just tells white lies or exaggerations either to try and cover up the extent of her gluttony and laziness, to justify her crappy behavior, or to try and deflect peoples' criticisms of her on social media. Assuming her claims of past abuse are false (which could go either way honestly) I still wouldn't say it falls into the realm of pathological lying because she isn't inventing outrageous, detailed stories - she's just making vague, unverifiable claims so she can play the victim to excuse her shitty behavior/lifestyle
That's the thing about pseudologia fantastica though, it's a subsetsubset of pathological lying and is very much not the same - the lies are often made in order to protect oneself from reality. Children of abuse and neglect are most likely to engage in it as a method of survival and fitting in, as they have no basis for what is normal. And while they can make themselves out to seem larger than life, it is also true that they will exaggerate the details of their life to gain sympathy and attention. My guess is, ALR couldn't cope and so she owned it. And then some, once her friends and their families would shill out the love and affection.
The delusions, to me, seem like this (and magnified by narc qualities)
She's always the victim because she can't handle that she's a terrible, manipulative human being. (And she's a narc)
She's fat but healthy because she can't handle the fact that she's eaten herself into a state of disrepair and death.
She loves youtube again because she's realized she literally can't do anything else to support herself and has no one to fall back on or a safety net.
She's denied health problems because they weren't physically obvious, because to admit that she was wrong is impossible for her as a narc. And she's only admitted small things recently for the sake of Victimlynn and subaggedon.
She knows she's lying, but part of her is desperate to believe it because reality (as it has always been) is too much for her. So she makes up a life/persona and "lives" it.