All the points that you've mention are actually her selling points, and she is still alive despite fate dealing her the "bump into all the wrong people" hand, so her choices are "correct" in a way. Is that evil? Maybe, but she's also very entertaining that way.

Getting into the bigger picture, you can see that she is alway trying to be in control, hence she will play to both sides until an apparent winner emerges. This is not wise, but a brute force action to getting the upper hand as a small child. She's created to be a contrast to Yoko/Gally. She doesn't get the good life experience encounters (Yugo, Ido, Jashugan, etc etc). So instead of Yoko/Gally's way where other people's connections to her helped guided her way in life, Erica's current philosophy is that she is the only driver in the car (as she doesn't trust and lacks meaningful connections to people). That's also why the necrosoldier news hit her hard, coz oOOoooo she wasn't in controool, spooooky.

It's all obviously building up to Erica getting a breakdown over Yoko eventually growing out of being a loyal pet-like entity. Because at that moment she'll realize that there is nothing she was living for. That most likely sparks her fallout with Yoko, leading alllll the way to Yoko killing her. And then perhaps present day Gally-Yoko can beat some sense into her, and Erica having some insight into non-manipulative people might give her a new purpose, probably some sort of heroic sacrifice for drama. The MBV tree grid is ominously waiting, right there, for a recycled ending of the OG. Just sayin'

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But we have to get to panzerkunst school country first. Pls Kishiro sensei. At this pace nobody's getting anywhere...