Well we've been over it today and she has always been a little less active than the other chicks, but having had no experience with raising chickens and even less experience with banties, I just assumed it was because she was so small. It didn't quite look like she had spraddle leg, but she was quite a bit pigeon-toed. Again, I just assumed it was the breed and those 5 little toes. She was the only bantie next to standard chicks, so perhaps what I thought was normal was actually a bit runty for a bantam. There's a lot I can pick out in hindsight, but I'm thinking perhaps it may have been something that was there from birth.
I picked out a beautiful perennial that I'd actually never heard of (Gayfeather!) because it looked a bit poofy and scraggly feathered like she did. I'll be planting it first thing in the morning.
Spending time with the other chicks has made me feel better, but it's just been hard for me to take. Having pets you always have to learn to deal with these kinds of things, but, for me personally, it never gets any easier.