Well many vets just don't see enough snakes to get experience with them, so maybe try to share (tactfully) what has been suggested & whatever seems to be working so your vet learns too.
Depending on what this is, the topical medications might not penetrate the skin enough to cure an infection, if that's what this is. (the swelling suggests infection, to me) And if you got a broad spectrum antibiotic cream from the vet, you don't likely need the others (OTC products that we suggested) in conjunction.
On the other hand, IF this is a burn (if you find where & how this might have occurred?) a better topical medication would probably be Silvadene cream. Safe & used as directed topically on snakes+.
"SILVADENE Cream 1% (silver sulfadiazine) is a topical antimicrobial drug indicated as an adjunct for the prevention and treatment of wound sepsis in patients with second- and third-degree burns"