Wry neck treatment suggests no more than 25mg of selenium, but it doesn't indicate what the strength of the Vitamin E is in that supplement you posted. You would probably be safer to just use a straight vitamin E 400iu capsule and shave a sliver off a selenium tablet.
I believe Bibby will improve, but if it's genetic, she may need treatment again from time to time. If it turns out to be a crop disorder, that too can be symptomatic of another problem.
I have had favorite chickens that I knew had an incurable underlying problem, but as long as they were behaving normally in every other aspect, I would treat the symptoms to extend their lives. At the first sign of decline, though, I would watch for that moment when they needed to be euthanized to prevent acute suffering.