Same, I really can't put my finger on why I don't see Sara romantically. I like her so much better on a friend path than romance.
I actually don't mind her on a romance path, but she would never be a first (or second, or third...) choice. I don't think there's really anything in the story there that naturally says "let's move this from friends to lovers", so the only reason to do so is for the lewd content (which is decent) and then the promise (that
better become a reality) of involving Ash in the relationship, at least sexually.
As far as looks go, I just really don't like the darker, centre-parted hair she starts out with, I don't think it suits her at all. And it's weird how different it is compared to her hair once you get on the romance path. Style is one thing, and I think she says about wanting a change in style, but the colour is also suddenly lighter and I didn't get the impression she had dyed it as part of that change (I might have missed this though).