Hi Mary,
Just caught up with this again... Is the vet a new graduate or inexperienced? When lab results come back, they say specifically what the lump is, and give every bit of info required, so the vet should not need to check with another vet! If you go a day over on appointment, that is not a problem at all. Make sure you opt for the vet you prefer... I always do! And don't be afraid to ask them to clarify things to you. At the end of the day, they are providing you with a private health service, and you, as a client, are the priority, so ask away and get them to explain things clearly... I know a few vets that like to 'talk technical' and this is often no help to the client!
It sounds entirely like Bonnie's been licking/chewing the lump - this causes swelling and possible infection. I have never known of a lump come back that quickly... most likely tissue swelling due to Bonnie messing with the surgical site. It really is important for cats/dogs not to lick/chew... which causes no end of problems, so I think it is that. Cat's mouths have so much bacteria, it can get infected quickly and swell to form a 'lump' type appearance.
If you have an appointment with the bloke vet... change it to the lady you like. Don't hesitate, honestly. Bonnie is the priority, and you are also being her owner. From what you've said so far, I just think the male vet doesn't seem that experienced...
Liz xxx