Got her into the vet this afternoon. Her lesion is now about an inch and a half in diameter, and starting to look inflamed. The outer part of the lesion is a bloody red mix of hair and god knows what (well, blood, I guess), and the inner part has crusted over and is starting to look pleasant. By pleasant I mean not pleasant.
So, today she got an injection of antibiotic (she fought it and broke the needle the first time), they took a culture around the lesion (she really didn’t like that, and started hissing at the tech). She’s usually really good at the vet, since she’s been there every month or two all her life, though she didn’t see her usual vet. So now I’m on twice-daily wound-cleaning duty, in addition to twice-daily antibiotics and antihistamines. She remains sluggish, but affectionate and has a good appetite.