Tiffany once told me that the scar on Jo's cheek had been misrendered by Wes (though she hadn't had the heart to gripe about it, seeing she got free art). The scar Jo has is basically a stylised claw marks, as if 3 talons had scraped their way up from the line of her jaw and midway toward the nose.
Also, from what I see of the avatar JoMidori took, the braid isn't something going down the side of her head, but rather gathered up straight behind. The braid looks significantly long, probably going down to the middle of the shoulderblades. It's likely the braid itself is a thin, tightly woven affair rather than something cute and fluffy like
Teletha Testarossa.
The ears seem like an important trait too. They're basically like furred cat ears, but positioned to the side where the normal human ear would be. Wes (oddly) seem to prefer the non-furry, almost elvishlike version of the ears (which you can see on the banner above with the green haired lady). However, descriptions seem to rather indicate that Jo's ears would be catlike and furred white. I'd suggest using
this comic page as a reference for the ears: I've always sort of saw the basic shape and look nekovalkyrja ears that way myself in my head.
Significant other little detail: Nekovalkyrjas like Jo have three fingers and an opposable thumb instead of the normal human four and a thumb (4 instead of 5). I'd recommend, if you're keen on your hand structure, to see it as the removal of the pinky and a resizing of the fingers (longest to shortest: index, middle finger, ring finger - proportion being: longest = human middle finger length, shortest = human ring finger length).
