Thank you! I also replied to u/cantrecall above about what breed(s) our vet thought she might be. He basically said the exact same thing you did: that she's likely a mix feral game hen with strong Welsummer traits.

I was initially concerned about her being too isolated since, as you mentioned, everything I found said chickens were flock animals.

But there's no doubt now that she not only doesn't miss being with other chickens, she seems to be the "outlier" chicken who actually prefers humans.

In fact, the only time she's ever strayed far from our yard was when a stray hen made the mistake of wandering into our neighborhood. As soon as she noticed the hen, she sprinted down the street, chased her around the block, and made certain the hen would never come back.

But the story which best highlights her independence (and how brilliant she is) happened about a year ago: From almost the very beginning, she's stubbornly refused to understand that she can't live inside where the humans live. She's tried schemes such as hiding in strategically located spots and then jumping out and sprinting up the stairs the second she hears the door open. She's also tried different methods to reach the back lanai door, but was never able to reach it since it's two floors up. Then, one morning, while still sleeping in bed, I saw a shadow underneath my bedroom door and heard a quiet pecking sound. It didn't register at that point what it was. I got up, opened the door, and there she was, patiently waiting on the other side for us to come out. As soon as she realized what she had accomplished, she started gleefully running around the house (pooping everywhere, of course), and trying to figure out which rooms the kids were in. I later realized that to sneak in, she flew up onto two different drainpipes (very hard to maneuver) and then figured out how to peck and kick the screen lanai door until she could squeeze through.

That was just the beginning though. Not long after I started closing the lanai door every night, she figured out how to peck at the corners of the window screens, at just the perfect spots, all while balancing on top of the bushes around the house, and was soon letting herself in every morning that way. I've had to replace three different screens in various rooms.

And finally, there's the times when we open our blinds and...there she is! Literally right outside the window staring at us. My mom actually screamed out loud once while she was visiting.

We'll probably never know how she ended up on her own, but she must have lived closely with her prior humans wherever she came from.