Good luck with this. As far as any remaining swelling, you may already know that snakes have solid (not liquid) pus, so it doesn't drain as in most creatures
(including us); instead it tends to wall off into a lump that can only be removed surgically. Whether or not I'd put a snake thru a surgery for a minor remaining
lump is something I'd only decide after talking with a good herp vet. It might be best to "leave well-enough alone" (as you said a biopsy & culture was done &
came back as clean?), whereas a surgery on a snake's face (so close to brain & essential to eating) carries risks that may (?) be best avoided. Up to you & your
vet(s). You say it's "not healing" but it appears to be? It's just that there is still some swelling, I assume that's what you meant? Do keep us updated...