Do you know specifically what test they did, that confirmed Marek's?
I'm asking because it's uncommon for most vets to run it, it's a PCR test that usually has to be sent off, and I'm only aware of limited resources that do it. I could be mistaken, maybe things are changing, but just want to verify. With Marek's and paralysis it's caused by tumors on the nerves, and I don't think pain meds would suddenly make that go away. Again, I could be wrong, but not what I have seen. I'm wondering, since it's a silkie, if it's more something with inflammation in the brain that is getting knocked back by the meds. Silkies and other vaulted skull birds can have more issues with inflammation in the brain and brain injury. They are also more susceptible to vitamin deficiencies and those symptoms. Since she presented with issues when she was younger, I wonder if this is related to that. As @WyorpRock said, if it is Marek's, they have all already been exposed, so unless you see severe issues affecting her, I personally wouldn't cull. In addition to the pain meds I would do some vitamin supplementing, E and selenium, and a b complex. Give her some time, and see how it goes.