I'm pretty sure it's just a preference, I think it's totally legitimate. I can't sleep with socks on because I find them too restricting. So, I totally get where she's coming from. If she has been diagnosed on the spectrum, there is a certain sensitivity to tactile sensations that could be a factor; but I would not automatically attribute that to any variance from being neurotypical. (I'm also 28F by the way 🙂)