I don't think alcohol or drugs has anything to do with it, although they may magnify it to some degree.
She is really remarkable in her relationships with others. First of all, she has to rename everyone in her life. So, mom becomes Schmee, Malan becomes Bibi, James becomes Peetz. I wonder if Rina is a real name? That covers just about everyone she has been with in the last four years. She even renamed her mangy cat.
At first, I assumed she renamed them to protect their identities, but I discarded that notion long ago. She really renames people, and actually calls them by their new names.
This alone is very weird, and suggests the level of control she must have in her relationships, which are always based on manipulation.
She then cultivates a whole new manner of speaking to each. With Bibi, she would speak in a breathless babydoll voice, sounding like a cross between a geisha bar hostess and a jailbait temptress. With mom, she reverts to a cutie-voiced six year old. With Peetz, she goes into her chipmunk faced, teeth baring, you're-in-on-this-joke kind of silly girl. With the only other type of person she has direct interaction with, drive-thru window employees, she uses a supersweet and polite feminine voice, even if she is in the middle of a roaring chimpout. She does the same thing with her viewers too, using soft, girly voices to read their names as she bitches her way through another angry rant.
All of these personas are disturbing to any casual onlooker except the dum dums in her audience. They reek of infantilism, misplaced sexuality, autistic oblivion, and hardcore manipulation. I am sure she is convinced these personas are adorably cute, and she has honed them (clumsily, of course) for decades. Due to her long-term social isolation, they sound absolutely batshit insane to ordinary people.
I believe that a number of factors are involved in these personas, but all roads lead to a desire to manipulate and extract what she wants. There are also elements of socially-isolated, autistic awkwardness. Part of it is also due to her being too dumb to cultivate an actual, real personality. Part of it is having no substance as a person. and her lack of anything meaningful or insightful to say. But driving it all is the attempt to manipulate; this is how she has extracted food, money, and favors ever since she was a very young child, and she has not attempted to change since then. So, in some respects, all of it is still being dictated by a very manipulative six-year-old girl.
Part of it is also for show (in which case, she is manipulating her audience). She spoke to Bibi like a little sexpot 15-year-old because she also wanted her audience to envy their torrid, hypersexy romance. She speaks to Peetz like an excitable kid because she wants the audience to believe they are besties and so in tune (since she lacks this kind of friendship with anyone else; I do believe she wishes it were with someone better than Peetz). So her various personas can be working on multiple marks at one time.
It is a significant part of what convinces me she is absolutely psycho, but it is far from the only thing. I still marvel at her little personas all the time. Homeless, shirtless meth heads ranting in the street seem less insane to me.