Would you see overgrown feathers as an indication of failure to thrive? I do not know about this condition if anyone can explain.
I also do not know the silkie breed, but those feathers look quite well developed if not enlarged, and that indicates parasite to some of my chicks. I see overgrown...
OP should listen to this advice. I agree she is looking at a parasite and as I said I doubt it is worms, so cocciadosis is an excellent candidate and somethimg I need to learn more about for my flock too. And I am sure I have lost many to cocciadosis and never realized it.
I was saying to...
Have you checked her crop at night compared to the others? If the crop is mostly watery, it could indicate worms which would explain the lack of growth. But I doubt you have a worm problem, just needs more development time.
To be honest your chicken seems fairly okay if she eats. Maybe just...