She must have developed insect bite hypersensitivity
. It is due to some insect bite, which usually takes place when we are sleeping.
If not treated in time, it may further spread.
Look for the presence of sting at the centre, and get it removed it if it is present there.
She needs prophylactic antibiotics, antiinflammatory drugs, antihistaminics and oral/topical steroids
. It will be better to consult a dermatologist
Dr. Ajit Singh Kulhari
MD - Skin & VD