My NT daughter definitely mimics some of her brother's behaviors. She looks up to him, she has always admired him, so I think it's natural. And, well, she is aware enough to know that my son gets certain accomodations from us and from school, and she would like those, too. Shoot, what child would NOT enjoy being told they don't have to do the homework as assigned to them? So, my talented artist daughter keeps complaining about how difficult it is to write ... um, well, we've explained to her that we'll work with her on ergonomics, on hand exercises, and so on, but that we really do not believe she has the actual physical issues her brother does, and she will have to accept that she cannot get the accomodations that he does. Once she realized no amount of acting could change that answer, things improved instantly.
I'm trying to think of some of the other things ... she has gone through a phase of chewing on her clothes like her brother does, fortunately it didn't last long. She tries to minic his lack of table manners ... but gives herself away by having perfect upright posture, lol.
As someone else pointed out above, some things just don't get minic'd. While my daughter may sometimes try to join my son in his pacing, because she wants to be with him, she has overall learned it's a private experience for him, and not uncovered any secret need to pace herself.
I was pretty sure by the time she was 3 that she was NT. Not positive; my son wasn't diagnosed until 7, after all, but fairly sure. While there were things she tried to do like him, there was just so much else that was completely different.
_________________
Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).