such as mosquito bites would be likely if you live in the area where mosquito bites are common and as children's skin is delicate, they appear as red small bumps.
An antihistamine syrup and a moisturiser cream should suffice, but if picked or scratched will release the watery liquid (flitrate from capillaries).
I am not sure what allergies she has (as you have not mentioned) but the above treatment should be enough.
If there is fever
, blood tests would be required that would depend on the geographical location to exclude the current viral outbreaks.