Thanks for writing in.
It can be allergic reaction
or irritant contact dermatitis
She can apply calamine lotion over the affected area and take Tab zyrtec for itching.
Avoid sun exposure.Cover the area with thick clothing when you are outside the home.
Antibiotics are not needed .Oral and topical steroid
may be needed based on severity of the condition.
With images of the affected area and details of the symptoms a proper diagnosis can be made.
Images can be uploaded by the premium questions area.
I encourage you to visit a qualified dermatologist
for proper diagnosis and treatment at earliest.
Hope this helps.