I think Ami would have worked better if she was shown less angry and aggressive, but more sad and scared. We got little moments here and there, but they were usually always overshadowed by follow ups that did shine her just in a bad light. And Sel could have still get angry and aggressive scenes, but imo he should have done it after making it more clear how scared she is and how vulnerable. That way people could understand why she is angry, why she acts like that. I mean sure, we know she lost her parents and akira is all the family she still has left and loosing her parents left her scared. But all of that was true from the start of the game. While she totally lost it just recently.
You mentioned showing how scared and vulnerable she is, but don't the scenes where she visits her parents perfectly exemplify that? Where she actually allows herself to properly show her emotion and act as a kid again?
The reason why she normally doesn't do so is because she's looking after a 30+ year old manchild who can't even properly take care of himself, much less anyone else. She cooks, cleans, and babies him... almost like a real mother. Not to mention that this dude has the mental fortitude of newspaper, constantly has schizo episodes, turns into a vegetable for months at a time, and tried killing himself in the past. The phrase "stay strong for your children" pretty much describes Ami, with the child being Sensei.
Everyone is a threat because as she said, they don't really understand Sensei, and might end up mentally fucking him, which, as she knows from the past, is very bad. She acts so aggressive because she wants people to stay away, because even if the people don't mean to they will eventually hurt Sensei because they don't really know him. And again, Sensei is all that she has left. If he dies, she'll be alone - and you can see from the scenes with her visiting her mother/father how scared she is of that.
I think she has very consistent characterization. And this recent breakdown is her realizing she can't be the one for him: she can't protect him when she's so flawed herself, and that she might actually be the one inadvertently hurting him.
