I just reread your post...... I would hold off on the antibiotics until after you worm her. You may find that is all she needs. If she shows improvement you should consider worming all the girls.
I think you are on the right track by worming her. I wormed my hens last month with Safeguard. They are going through molt and look much better this month.
OP says she has not seen her eating or drinkng. A chicken that is cold enough to not eat and drink should be ravenous when brought into the house and warmed up.
edited by staff
I would say if she is cold and not eating that is absolutely necessary to warm her up to see if she gets better. This hen needs a good check up - looking at body condition is a good start. Is she thin? Is her comb pale? Is she eating this morning? Are any other chickens acting like her?