Vitamins for older cats

[EmbraceTheSarcasm]

Is there anything I can give a 20yr old cat to improve her condition? She was at the vets recently for a check up and got a steroid injection. Will a pet shop sell anything decent or could she have cod liver oil on her food or something?

Our cat has recently finished a course of vitamin B12 injections as she was found to be deficient. She has certainly perked up so shows how a deficiency can affect them. She's younger at 13 though. However, I don't imagine a vet would do without checking the animal needed it.
Have you asked your vet or vet nurse if there's anything you can give? I wouldn't have thought cod liver oil would be advised but I could be wrong.

I went to the pet shop and got some "conditioning tablets". They are mostly brewer's yeast and so contain B vitamins. Crumbled onto her food.