I can understand your concerns,The history suggests that your child is having episodes of Acute Urticaria
and as you said it is getting better with anti histamines
,that is supporting it further.
1:I would like to add here is you should carefully examine the ingredients in her food and also any medications like anti biotic so that if something is causing it she shouldnt have it in future.
2:If she is running a fever with a rash then again it can be a viral infection like Roseola
and needs to be reported at once.
3:If there are symptoms like hoarseness
of voice or tightness in the throat or swelling of face and lips then take her to the emergency without a delay.
Otherwise fix an appointment with your dermatologist
and discuss the issue.
I hope i made my self clear.
thanks a lot .