There are, as you have seen from dr google, many causes for a head tilt.
Many farmers are coming into our vet practice at the moment for vitamin b1 injections for ccn, which is very common, and would appear to be rife this year.
Low calcium is much rarer in sheep than cattle, but can happen after lambing, so v. unlikely in a shearling.
Listeriosis would not have responded to vitamin injections, but can be picked up from the ground or infected silage through small cuts in the mouth, so could theoretically be affecting a shearling, though i might expect to see a droopy face or dropping food with that.
I have never seen vestibular disease in a sheep, and gid, where worm larvae encyst in the brain is not that common either.
With the symptoms, the prevalence this year, and the response to vitamins, it is probably ccn.
I would repeat the vitamins daily for 3 days and she should come right.