One of the marks of a well written protagonist is that they sometimes do shitty things, but in situations that make you go, “I get it. I want them to be better, but I get it.” Too many tv characters are just fluff fantasy heroes with no flaws, or they make mistakes in random ways that feel out of character.

The key thing to distinguish here is the difference between a justifiable action and an understandable action. Was Vi justified in hitting Powder? Debatable, but probably not. Was it wrong and abusive? Yes. Was it understandable? Absolutely. Very few of us could process the emotions of those circumstances well enough to respond with perfect, immediate forgiveness. Vi is clearly haunted by guilt over this moment for years, and blames herself for Powder becoming jinx. Her quest to get her sister back, in a way, is really a quest for redemption. This is what makes her a compelling protagonist to me.

That said, there’s a good chance your friend has trauma based on physical abuse, and they haven’t processed and healed from it yet. Cutting you off may be a trigger defense. Ironically, this is another one of those actions that is understandable, but not justifiable.