Advice for my sister's cat.

[Thorn]

Poor kitty...have you tried something like Feliway? e.g., http://www.drsfostersmith.com/produc...tid=8906&rel=1

One of the behaviorial pet people swears by it for stress related behaviors. Doesn't work for all, but apparently enough that professionals don't discount it as nonsense.

But, I'd still try to get that cat into a vet...could be an infection by the symptoms you describe.