That presumes, incorrectly, that the point of Sophia visiting the salon is that she feels the need or want to change her hairstyle. It isn't, and is likely just an excuse. Even if she does change her hairstyle to one of the latest Daz models, it's likely going to be something very similar to what she has now, with the excuse something along the lines of "since you're here, why don't I just give you a trim?" Sophia's in-game reason for going to the salon is as far as I'm aware, just to catch up with Claire, since Sophia so far only has a few friends. Keep in mind, many women just enjoy an opportunity to talk and gossip.
Dylan might not even get a new hairstyle, since to my knowledge he's shown no interest in changing his hairstyle. He didn't even want to go to the salon in the first place, so like the Yoga event, I'm perplexed why he'll be there at all, apart from some excuse to set up Dylan/Marie, since for whatever his reasons L&P wants to.