You could try tube feeding if you want to learn. Here is a good link about that:
https://www.backyardchickens.com/threads/go-team-tube-feeding-updated-12-29-2019.805728/
It looks like she has wry neck (torticolis,) a neurological symptom. It can occur because of a head injury, a vitamin E deficiency, and is seen in certain diseases including Mareks. Silkies tend to be prone to it. I would get some human vitamin E 400 IU softgels, and give her one into her beak...
If you mix the Corid, she has to drink it to get the benefit. Corid dosage is 2 tsp of the liquid, or 1.5 tsp of the powder per gallin of water for 5-7 days. Have you ever tube fed a chicken? First I would work on getting her take it herself. Try her separated maybe with the 6 week old to see if...
Is she hunched up or puffed up and lethargic? What do her poops look like? Will she drink if you dip her beak? I would try some wet chicken feed plus water to make a warm mash. Add just a little egg to it and offer it. If you think she possibly is getting coccidiosis, try Corid.