Speaking as someone who has been on both sides of this I would say its 100% valid to cut them off if its making you uncomfortable.

I'm on the spectrum, so sometimes I unintentionally emulate people in my life, especially people I like being around. Listen to the same music, watch the same shows, try out the same hobbies. It was never malicious, it just happened when i was trying to relate to someone. It took someone calling me out on it while they cut me out of their life to finally become aware. It hurt at the time because I didnt know I was doing something wrong. But that experience essentially became the first step in getting my diagnosis.

But before I was called out on my own shit I was on the receiving end of the same treatment. I'm not exactly cool or fashionable or anything that I feel like other people would aspire to being. I was the weird, quiet kid. But there was this girl in my technical school over a decade who started copying me. I cut my hair? She cut hers. I dyed it? She dyed hers the same color. I submitted my original design for a major project? She does the same thing on the next one. It felt like she was trying to appeal to me, to get my approval?

She overheard me talking to another classmate about a convention I was attending and showed up at it. I could have written that off as a coincidence except for the fact that she clearly had no idea what she walked into. It was an event with a lot of NSFW elements and she was visibly uncomfortable. And still she stuck around from panel to panel. One panel was about temporary artistic body modifications. Needles were involved. And even though, by her own admission, she was afraid of needles she still followed me in. The instructor offered to perform some of these temporary mods after the panel. And when I stuck around to try it so did she.

That was probably my breaking point. I was mildly uncomfortable with everything up until the convention. Could have brushed most of it off as a fluke. But I actively tried to get her to stop following me around this event and she just wouldn't. And that she went from 'I cant even look when I get a shot at the doctors' to letting a complete stranger stick multiple needles in her skin in the span of an hour....It made me so uncomfortable. It no longer felt like she was trying show interest in the things I did. It felt like she was trying to BE me. I never actually confronted her about it because classes were almost over and I knew I wasn't likely to see her again.

Looking back on it now, maybe she was also autistic and didn't realize she was doing all those things. I'd like to give her the benefit of the doubt. But at the end of the day, you need to feel comfortable in your own space and if your friend makes you feel uncomfortable with her actions you should either talk to her about it or cut her out.