Hi hun. I would call the pedi to let them know this happened. Chances are they are going to just have you monitor her and give benadryl.
Owen just had his first allergic reaction last week - to an antibiotic and it looked EXACTLY like this. We were told not first, not panic
. Second, to give benadryl every 4h regardless of itching or presence of hives, for 48h. Third offer an Aveeno bath if he seemed to have break through itching.
I don't think it itched all that much. But it certainly looked horrid. They told us that he could continue to have hives for up to 14 days, even though we obviously were not giving him the offending antibiotic anymore.
Naturally monitor her, if she gets more hives, has difficulty breathing, blue around her lips, swelling/hives on her face - I'd call for an ambulance. However, I doubt any of that will happen. It does take some time for the offending substance to leave the body, and then for the body to calm down and stop pumping histamine like crazy.
Hope this helps some.
PS she could be sleepy and have peed through her stuff last night because of the benadryl... it makes Owen super groggy - perhaps her too.