Sorry to see you never got an answer! And very sorry to hear bout your sweet rooster!
What I would do is make a smaller amount then what it says. So what I mean is cut the recipe in half if that makes sense. You will have leftovers.
Do you add water to this?
Yes, she can grow them back if she hasn't finished her molt. Do you have a plate heater you can put in the coop? Maybe keep her inside until she has settled down to insure she doesn't get an infection.
He could have swallowed something that got stuck or he is stressed. Has he been eating?
Do you have a bigger cage to put him in so he can hold his head up better and straight ( that will also help him breath better).
Sorry to hear your hen is having trouble!
If you no longer have rooster, they could be picking at each other due to change of pecking order. She may not grow those feathers back until her next molt.