That is not arthritis I have a 9yr old duck with arthritis and she limps but doesn't fall around like that. That makes me think neurological or toxin. Anything in your yard or garage she could have gotten Into metal or some kind of liquid or plant material?
Any chance you can have a vet look at her? is she your only duck? Does she seem confused [lost]
Any chance you can have a vet look at her? is she your only duck? Does she seem confused [lost]

