You should be able to get it at the grocery store, or a pharmacy. TSC probably doesn't have them.
Poor girl! I'd definitely get vitamins into her as soon as possible.
I'm glad your other chicken is doing okay!
I don't think medicated feed has them, if they did it probably wouldn't be enough vitamins anyways.
Yes, try giving her some eggs.
Welcome to BYC!
Are any other flock members exhibiting similar behavior at all?
What I'd do is get vitamin E 400IU and 1/3 of a B complex tablet and give her those daily for a week or so. Also give her eggs to help her absorb the vitamin E.
Hopefully it's nothing serious!