ouch nasty! At least you know your cat was not the one that started it cos the bite was as she was leaving...
Cats have nasty bacteria in their mouths, and their teeth act to inject these deep under the skin/muscle. So even if a bite looks mild (ie. one or two punture wounds) it can turn very nasty. Depends on where the bite is and how deep and how manky the other cats mouth is to how bad its going to be.
I have been put in hospital by a cat bite (IV antibiotics for 2 days). Even after downing some augmentin as soon as I was bitten, and two penicillin jabs (in the butt!! :oops: ) the next day didn't stop the infection from progressing vy quickly. The cat that bit me had a horrible stinky mouth and was about 16yrs old, so not surprising.
I also met a lady who got bitten by a cat, but then a couple of weeks later got septicaemia from it as she didn't take the bite very seriously.
I wouldn't get all lynch mob on the other cat tho - all outside male cats fight at some point -even well cared for neutered ones - and it only takes one bite to cause an abscess. Only way to control it is to keep cats inside at night, especially dawn and dusk.