
Same here, if our Vet removes any lumps that he doesn't recognise or know what they are, he will ring you and ask you if you want it sent to the lab. He always recommends that you get it sent off for a diagnosis, especially as some cancers are more aggressive than others.
I'd have thought your friends vet would have given it a wide margin on excision and sent off the surrounding tissue just to make sure it hasnt metastasized.
It could always just be abit of swelling from the wound, rather than a return of cancer, but I definately wouldn't leave it too long for a second opinion. Hope she gets on ok. :(