How does Buzz react to her nipping? Do you stop it every time, or does she stop on her own?

If she is obsessed with this one particular spot on his face it must have to do with the medication that spilled on it. A rabbit’s olefactory abilities are quite amazing. I really don’t think 4 hours apart would break your rabbits’ formerly close bond. It is most likely the strange scent that is throwing Sweet Pea off.
Could you wash the area above his nose and then apply other scents, like banana, or Sweet Pea’s favorite’s fruit scent? Keep putting them together under your supervision. She will get over it with time. Don’t give up.

The banana trick has always worked wonders here, also when Jack had been to the vet and Molly was a bit upset about it.

I’ve heard about putting scented oil on the bunnies before so they smell the same. I haven’t tried it, but I’d assume it would work. Give it a try and let us know.

Take a bit of banana and mash it and then smear it loosely on the forehead and maybe the ears. And then show it to the other bunny. The thing is that the bunny with the banana on can smell the banana so give some to his one also. Only do one bunny with the banana at a time otherwise it will be chaos.

The banana will dry up and be difficult to get out if the other one doesn’t lick it off. But just wet the area and brush it and it will come off.

Think about who’ll you put the banana on…eg. Molly doesn’t lick anyone at all although she loves banana, so for me it has been a waste (and a mess) to put it on the others hoping she would lick it off. But it has worked well the other way around.

This sounds exactly like what our female (Pixel) is doing to our male (Chibi). Chibi is older by a month and has been neutered for over a month. Pixel is waiting for the proper age to be altered. It’s her habit to always groom his head, chewing and pulling chunks of fur out right down to the skin. When they get together she always meets him with the submissive position and he always ignores her request for grooming. Usually, he’ll work to force his head under hers until she gives in and grooms him. That’s when the chewing starts. She’ll then come over to chew him at regular intervals throughout the day, even if they were laying or playing in separate locations. He never runs away from it, though. It feels to me like she is annoyed at being snubbed and is getting back at him. It also seems like he’s letting her do it to keep the peace. We’re both hoping that this behavior will stop once she’s been altered. At least her sequestered recovery time should give him the chance to grow his fur back. We’re tired of him always having a ragged hole in his otherwise handsome face!

Nippy grooming can be seen during a bonding but should resolve between two altered rabbits over time. If the rabbit that gets plucked does not run off,  you should intervene.
My Neigey was pinching Lint all over but sometimes got obsessed with his face too. With Neigey I could stop him with tapping on his forehead, and pushing his head down to check him. It depends on the rabbit, but it might be worth trying on Sweet Pea.

What happens when you let the biting go on? You said she just plucks him, never breaks the skin. Will she stop on her own?

This is a really long shot………..and something you probably don’t want to hear – sorry!

Given his history with dental issues, could she be picking up on some abscess activity?  A “long shot” like i said!

Thanks for adding the update. It’s good to read the conclusion to these things. It may well help someone in the future who is experiencing something similar.
Well done for persisting as it paid off. Good on Buzz too, for putting up with Sweetpeas moments!