Umm, length of hair and nails are key indicators on the scale of "butch" to "femme", and that IS a universal standard. It has nothing to do with what I like and much more to do with the fact that Selina Kyle is traditionally very femme, often to an exaggerated degree, and her current look flies in the face of that history with a much more androgynous look.
And while you might find that look "practical", and preferable, it remains out of character for Selina Kyle. And that's the point.