What a cutie!
She not only looks pretty dark, but has practically no side pattern that I can see. There might be some subtle morph floating around in that breeders lines that he is unaware of or it could just be a one off. I'm not even sure off the top of my head what morph it could be. Many of the darkening genes would be making the pinstripes larger and more wobbly looking. Woma tends to drastically reduce side pattern in Pinstripes, but not to that degree, and I don't think it causes darkening. Most of the other things that reduce pattern would lighten, rather than darken her. If it's an official second morph, I don't think it's a very common one. Spider causes a lot of pattern reduction in Pinstripes but they tend to have white up the sides a decent way and some thin stripes going across the dorsal, not just parallel to it, along with badly broken up pinstripes.
Maybe someone else might have a guess, but as far as I can tell it's not something common.