K.K.
My son experience chronic hives. They are stress induced, so anything that upset teh normaly ranges for his body set him off. We have had to use antihistamins year round to try and reverse how quickly he reacts.
Clariten and Zyrtec have worked well. Mountain ceder is very high right now to.
Remember each time she breaks out the next time, maybe cover more an area, come quikcer, stay longer, etc. I would keep her on antishistamine for at least three weeks.