Cat now fighting with her sick sister

I recently took one of our cats, Kupo, to the vet to get her eye checked out. They kept her for the day for blood tests, then gave us eye drops to administer every 6 hours (plus they gave her a deworming pill, stupid first vet didn't even check for tapeworms )

So that night we brought Kupo home, and ever since her sister Tanuki has been hissing and growling at her at every turn. She'd never been aggressive before, Tanuki was actually the submissive one.

Has anyone seen this before?

Will it stop when Kupo's off her meds?

Should I shoo away Tanuki when she's being aggressive?

Help and Thanks!

Kupo smells funny to Tanuki; it's not just the medication, but the fact that one cat has been to the vet's and the other hasn't. (Also, Kupo may smell "sick" to Tanuki, which makes Tanuki want to stay away.) You could try the scent-swapping techniques outlined on this forum for introducing cats to each other, or dab a bit of vanilla extract under their noses to disguise the strange smells. Once they get back to recognising each other again everything else should sort itself out between them. Good luck!