That's way to young.. and as someone who bred them for a number of years, I'd be surprised to see Silkies come out alive under that plan.
This IS the
root of your problem, but possibly not the entire issue. Definitely a good place to start!
The vet will charge you and you won't really get any different answers.. so you do what's within YOUR resources and comfort level!
You can use
starter feed only.. all the way until everyone is laying as long as you put oyster shell on the side free choice once you have layers. OR you can use any
flock raiser,
all flock,
grower, etc.. The main difference in all of them aside from brand is protein (amino acid) and calcium content. Don't go below 18% protein for them Silkies. And not more than 2% ish calcium when not in lay.
With a mixed age, gender flock.. the best choice is one of those. I use Purina Flock Raiser with oyster shell on the side for active layers.. I never switch feed (to layer) or worry about different ages. Using something that's available regularly with a mill date under 6 weeks prior (good turn over) is one key since nutrient oxidize and diminish with time.
Throw a hail Mary.. give her liquid yolk, if you got.. that's what get's chicks going when they come out of the egg and sustains them for 3 days.
I'm not sure the nutrit drench is the best choice in THIS instance.. Just wanted to know what you had on hand or available (please review nutrient and make an informed choice) Rooster Booster makes a couple other products that are superior to the one mentioned.. Poultry Cell and Poultry Booster.. But I would likely mix the one you have now at it's maximum dose and use over the next day or so.. she won't starve but hydration is KEY.. how are you getting things in her? This link has some suggestions.. including that it might be thiamine and not riboflavin that I should have have been asking about..
https://www.raising-happy-chickens....as 'twisted neck,backwards or towards the sky.