It sounds like you’re going to have to tube feed her. I don’t have any experience doing this, but I know 
@casportpony is very knowledgeable about that.
If you look into her beak, can you see any more lesions? I know it won’t be fun, but if you could try to get them out, you might be able to save her. They’re probably almost completely blocking her esophagus 
You’ll want to make sure none of your other birds have canker either. It’s got a very distinctive smell, as I’m sure you’ve noticed. To check for it, it’s pretty simple to just go smell everyone’s beak. Of course, it would be more thorough if you looked inside all their beaks, but that can be time consuming and not conclusive as you might not be able to see well enough.