The third option is that Peridot's somehow managed to become a wizard without every thinking about it, which Lambert seriously doubts is the case here, judging by how the EMPHASIZED TEXT on the blog post repeatedly assures visitors that self-transfiguration is a difficult task even for the most skilled of mages.

... He'd also meant that as a joke, mostly, so he feels a little bad she's taking it seriously now.

"Unless you're suddenly feeling the urge to drink blood and have a new allergy to daylight, I think you're fine," he says reassuringly. The 'shapeshifter' bit isn't all that helpful, either, but it gives him a few different things he can try searching for.