You have a tough decision to make. Only you can make it.
That said, I will give you my opinion.
I do offer supportive care to my birds when they are not feeling well, but I also take everything into consideration-especially quality of life. My goal is to do what I think is best for the...
How long has she been like this?
It doesn't sound like she is able to take care of herself and needs supportive care.
If you were to take her with you, will you have time to tube/syringe feed her several times a day, keep her bottom cleaned up, etc.?
What does your family think?
Can you take some fresh fecal samples to your vet for testing?
Photos or a video of her are welcome.
For the Silkie, it sounds like first priority is to take care of the lice and see that she is hydrated. Once she is drinking, then offer her some food. Layer pellets if fresh would be good...