Long story short, we clicked at first because we're both super nerdy. Over time she's started to copy everything about me just for a social media image (and this is not a blind assumption I'm making, it's been formulating in my head over the course of three years of her behavior) She is not the type to take criticism. She's very slippery, would rather cut you off instantly than apologize or self reflect.
Recently she latched onto this show I've loved since I was a baby (and I mean love, most of my usernames are after the main character) and started sending me videos of it associated with things I dislike. Ex. A video of the show's characters becoming an AI generative prompt trend. A video of a guy doing perverted things to the characters (they're both under 10 years old, btw.) I told her the first time to stop, and admittedly I could've been nicer about it but I'm very protective of my childhood and in the moment I felt deliberately attacked. She just did it again today with the second example, and I'm so mad I think I will genuinely cut her off.
The thing is she is the only friend I've kept after graduation (I didn't have a big circle to begin with) and cutting her off would leave me ultimately friendless. Would that be worth it for me? I feel like I should communicate this to her in case it might save our friendship. I know how I sound like a crazy person to everybody else, since it isn't possible to "steal someone's personhood". But this situation is very real, I know other people who have had friends that try to become them (sometimes to the point of stalking). How can I tell her how I feel without her running off? Or should I just cut her off now?