It wasn't just seasonal shedding. She got herself a skin infection.
The vet thinks it's ringworm, so she took some skin cells to watch for the next week to see if it is, in fact, ringworm. She gave me some antifungal ointment to put on the spot on Siren for now, and hopefully that will help. I have to bring her back in two weeks anyway, either because the test showed it's something else or to make sure the ointment completely cleared it up.
*Sigh. My poor fur baby.
I'm going to get ringworm now, aren't I?