Clean it with saline---try to flush all the "crumbs." It looks like dried blood to me. You might have more luck with the cleaning if you wet a piece of gauze with saline and let it sit on the area for about a half hour or so before flushing and wiping as that will soften and loosen bloody bits.
If you don't have a clear view of healthier looking tissue than I would leave the darker spot. I might chance it myself but would hate to give you internet advice that might leave you with a bigger issue. Hard to tell whether it is simply poor perfusion that might get better as she heals. Pack the cleaned wound with a piece of gauze (try to get non-woven gauze if possible)that has been soaked with saline and squeezed out a little---wet but not dripping. Don't put wet gauze over the whole area, just into the open area. Stuff it in that open spot---gently, but into as much open area as you can. Not jammed tight but not fluffy either. You can top it with a dry gauze pad and put a cute little shirt on Gretchen like you've been doing.
If you can get "plain packing gauze" in the 1/4" size that would be great. It is a continuous length of gauze that can be packed into a wound and cut when you're done packing. Easy to push into crevices with forceps or a tweezer. It comes in a plastic jar.
Change at least twice a day, more often if you see drainage coming from the wound. Wet the gauze thoroughly before removing---if it sticks, wet it again and wait. Pulling off a stuck bandage will damage delicate new tissue. Assess the area with each dressing change for color, warmth, and drainage.
Keep up the wonderful work and give Gretchen (and yourself!) a hug from me!