I think they're from that stuff I use in her tail, which I got on a brush and then ran over her body. It's all I can think of, as everything else is the same. It's so bad that she has edema on her belly.
Last night I gave her banamine, put her blanket on, and turned her out. I went back out this morning and not much had changed, so she got banamine and (after long conversations with two different vets) 20 25mg tabs of Benadryl.
I'll try to get some pictures of the hives tonight. Cross your fingers that the Benadryl made a difference and that there aren't any there, though!