Nice pictures, and good descriptions! Very useful!
Dunlap Hatchery has them too, but I agree they are not available at very many hatcheries.
Looking at your photos, I see matching little red wattles on all three Wyandottes, so I think all three are one gender (probably male.)
There is a gene that makes chicks grow their feathers much slower than normal. They are normal and healthy, just slow to grow their first feathers. So that might be what she has.
The gene is called "slow feathering," for obvious reasons.