I know this is way late in the game, but how did your Sumatra end up?
My Sumatra pullet is having the same issue. She is about 6 or 7 weeks old, and just a week ago or so she started walking around with her neck and head completely sideways to her left. She can still walk around, and I believe she is eating and drinking, but she loses her balance a lot. I have had no luck so far, I have been giving her Vitamin E tablets and Brazil Nuts mashed into a slice of banana (for the selenium, vitamin Bs, and a good consistency, and she loves bananas). I might try Poly-vi-sol if I can find any around this small town.
I hope it is not genetic, I was hoping to breed this pretty little pullet!