Hi, thanks for your query.
Your daughter seems to have developed urticaria
It can be due to food items like sea food, nuts, dairy products, or any other food,infection, infestation, dust, pollens, medicines etc
You have just given her benadryl
, so you can wail for a few hours, if it settles and no new lesions occur then you may not need to visit a doctor but if it persists and new lesions continue to appear, then you may get her examined by a doctor so that other appropriate medications can be added.
Hope this solves your query.