This is her sun bathing with her wing out. I'll grab a couple pictures of her neck as well.
To be honest I have never seen feathers like that. They are interesting for sure.
What you scraped off if most likely keratin which is normal, it's part of the sheath that the feathers come out of, the birds will shed keratin for a while.
I don't see anything wrong with your feed or treatment of wry neck. Mealworms will make a fine treat, just make sure they have access to grit.
The neck could be genetic so she may never respond to the vitamin treatment, but if she were mine I would keep it up.
It's possible the feathers could be a genetic defect as well, but I tend to agree with your suspicion that she may not be able to groom/preen because of the neck, this could why the feathers look like that.
Does she ever take a dust bath?
If she doesn't you may want to provide a dust bathing area - a loose pile of dirt will work, some people use a combination of dirt, sand, ash, etc. Dust bathing may help her shed the excess keratin a little easier, because chick do usually preen that out.
She looks young enough to where she will go through at least one more molt, so hopefully she will shed these and the others will come in normally.
If she is eating, drinking, pooping and seems to be doing well, then just keep an eye on her. She is a cutie pie for sure.
