For goodness' sake, folks. Here's a young vulture.
http://www.fotolibra.com/gallery/78657/turkey-vulture-chick/
Three major things that are different here.
First, vultures feather out differently.
Second, the body is carried differently.
Third, and most obvious, please note the head. Vultures, condors, and the like all have completely naked heads. This allows them to reach into carcasses without covering their feathers in gore. Their heads start out naked and continue to be naked. The chicken in the first post does not have a naked head because she is not a vulture.
Rachel could possibly be an escapee from a cockfighting operation, do you know if anything like that might be in the area? The feistiness and flying ability makes me think of Hawaiian feral chickens, a lot of which are descended from escaped fighting birds. Besides, that lanky, black-feathered frame with minimal to no comb looks a lot like Hawaiian feral hens, I saw several that looked exactly like her when I was in Kauai. Assuming you aren't in Hawaii, I seriously think you have a cockfighting bird there. I could be totally wrong, though, she might be a purebred of something more junglefowl-like, or just an odd mutt. If she is fighting stock, she could still be a perfectly nice bird. The hens in Hawaii get along with each other perfectly fine.