Yeah, I've certainly looked into the real stuff quite a bit as well. It's just... I know someone who used to be rather intelligent, but a side effect of them getting in a car accident and splattering part of their brains across the windshield was that they took a major IQ hit. They went from being a rather intelligent person, to being very close to a stereotypical ditz with a handful of mental problems. I've also met people who were definitely intelligent, but just watching them go through their OCD motions over and over despite knowing them fairly well was still cringeworthy.
Things like that just; well, they honestly just scare me. I place intelligence and mental agility
way up there on the "qualities of a person to know" list, and the idea that not only do things that interfere with it exist, but that they can actually happen to someone who didn't have them before? It really hits me. And the fact that fiction takes things in a more complete direction than reality does just means that they manage to slam
all of those aversion buttons instead of just some of them.
The end result is that I'm getting very conflicted messages. Half of me is loving the darkness and reveling in the extreme contrast that is being created between it and the cuter parts of the show (extreme contrast and genre whiplashes like that are honestly some of my favorite things in just about any type of story, be it anime, tv shows, movies, or books), while the other half of me is screaming "no stop watching it get away I don't want to think about this".
As for what she has specifically, it's difficult for me to tell since I've only see a couple episodes, and it's certainly exaggerated at least somewhat from what it would be like in real life, but it seems like the closest match for what she's experiencing would be some form of
Dissociative disorder, which is the category that includes things ranging from PTSD to having multiple personalities switching in and out. It also can include inability to separate fantasy from reality, memory problems, and hallucinations as part of its symptoms, which appears to fit what she appears to be experiencing. She's possibly even got the multiple personalities thing going as well, albeit being expressed through hallucinations instead of by directly controlling her. Though of course I haven't watched more than the first two episodes, so I'd need to put in another few hours before I could be more sure about that.