I'm not convinced that Bern doesn't know about her true self. I mean, you need to have a certain amount of intimacy to have regular sexual intimacy. And it's likely that these two have had more than a few off-panel experiences together.
I also think that Killer Chef (I forget her name, but the psycho girl who works for Tin Man in exchange fore creating horrible monsters) is wrong about Maytag.
Emotionally cold people seem similar to people with antisocial (read: psycho) personalities, but they aren't necessarily the same. In fact, I'm told that depressed people also often have blunted emotions. Maytag is cheerful enough, but we're not really sure what the "true core" is actually. Just that she's a bit bland emotionally, and also very driven and determined, but unlike an actual psycho, most of her drive appears to be to belong. To fit in, to have people like her and entertained by her. In fact, judging from her motivation to get through the Dark Cell even if her memory is gone, her eyes are gouged out, and she's in terrible pain, I would venture a guess that her desire to entertain is an authentic desire.
Maybe she's a sad and lonely person at heart, who hides behind a mask of deadpan (from herself), and hides behind another mask of split personality (from others). In fact, we've seen her actually crying a few times, and more even than her deadpan, it seemed real. When people decide they don't rust her anymore is when she gets must upset, and she seems happiest not cracking jokes but being
very honest.
Update: I don't feel that's 100% true, just as all outlooks have some levels of hypocrisy. She doesn't for instance starve herself or eat to obesity, or use most drugs aside from alcohol that I can see. Well, I imagine the potions probably antidote most drugs to the point that they're not fun anymore. But still, it seems her lack of boundaries doesn't extend to any sort of self-abuse. Probably because since she accepts most pain, trying to hurt herself would be vaguely like tickling yourself.