Greetings SueHasChickens,
It appears your chicken has gout.
Too much uric acid is being produced, but not eliminated from the body.
There are so many things that can cause gout.
Causes: feed/nutritional, vitamin A deficiency, protein exceeding 30%, chemicals, viruses, previous diseases, low water intake, pesticides, high antibiotic use and anticoccidials, even problems during the incubation period of the chick can cause gout in the future.
What can be done to help your girl?
Isolate her in a hospital crate or somewhere safe and out of drafts, so that you can monitor her. Provide good supportive care.
Diet: feed, fresh kale, and broccoli, shredded carrot, cooked sweet potatoe, toast with real butter, cooked egg. All these foods are high in vitamin A, which may help.
Therapy: coconut water (known for healing gout) or Apple Cider Vinegar - in her waterer for half of the day, then switch to fresh water.
Monitor her water intake, she needs to drink water to eliminate the high levels of uric acid.
I know it will be difficult, but try to figure out what may have caused her gout. There is also the possibilty that this may be something that you will have to treat periodically throughout her life. Take time to do some research of your own, you may find other things that will also help.
These are my thoughts on gout, I hope they are helpful.
God Bless and peace to you and your little hen.