Thanks for writing in.
The condition can be insect bite reaction,contact dermatitis
Also I would like to know-
Does she have any pain/itching over the area?
Since when she has this? Does it started overnight or progressed very slowly?
Is there any discharge/ scales over the affected area? Is there any skin discoloration of surrounding skin ?
Can you upload the photographs of the affected area?
Upload the photographs and answer the question and we can continue the discussion here.