I too live in CA and lost one to what the lab said was "suspected Marek's". He didn't have the classic leg positioning, but she couldn't walk, wouldn't eat or drink, and went into trances where I thought she was dead. I babied her for 3 weeks before she died. None of my other birds show any signs, and it has been about 3 months.
Campine Lover, if you lose your hen you can have her sent to a lab in Davis and have a necropsy done to see why she died. It is free of charge, all you have to do is take her there, or have your vet ship her using their transport service. That will at least let you know what to watch for in the rest of your flock. There will be a small fee for transport if you use your vet. Mine charged me 25.00 from Redding.
I'm sorry she is sick. It is so hard to know how to treat them. I did vitamins, electrolytes, yogurt, force feeding, scrampled eggs, baby food fruit, and just about everything else a chicken might like. I kept hoping it would go away.
I am still not convinced it was Marek's. So far no one else is sick, and I have a closed flock, and no chickens real close by. I am running a risk by not vaccinating, but I think that in the long run that breeds stronger birds.
Good luck, and I hope she gets better.