It takes quite a lot of ether fumes to do the job. It also takes quite a while to work. It should work, but how long it will take is unpredictable. I would still recommend cervical dislocation over ether. Ether is easier for us, but cervical dislocation is quicker for the bird. (This is the crux of the debate over whether ether is humane or not.) A quick snap of the neck or decapitation by hatchet, and it's over. She will never know what's coming, so it's over before she'll know what has happened. Perhaps you could knock her out with the ether then quickly snap her neck? Then you have anesthetized her so she won't feel anything.
I am sorry for you and your bird. Tough call.