Theirs a few alternate realities and certain points within the canon reality in which Duchess's mane and fur becomes overgrown for several different factors. One being that she becomes too busy to have time for such frivolous things as keeping her mane and fur short. Her human form reflects this by also having longer hair.

This alternate reality/time period version of her tends to be portrayed in a more mysterious tone that her usual one.

I might make a fully colored version of this at some point. But as for now, It'll remain a cute lil doodle.