Up to you obviously to do as you think need be done, but personally, even character design wise 18 chiaki has that childhood friend vibe that doesn't inspire excitement at the moment.
Personal taste aside. Already got one short haired gal with some heat to her. A short haired one that's timid lukewarm is... I think at the least leaving her hair long would make any lewd scenes feel more varied to what's available, visually speaking