Thanks for writing your query.
It seems that your friend is having dermatitis
. She needs a clinical examination.
She should consult a Dermatologist
She should keep the affected area clean and dry.
Clothings both inner and outer should be clean and changed daily.
She can apply locally cream conatining combination of antifungal like miconazole, steroid like betamethasone
and antibiotic like gentamycin. This should be applied atleast 2-3 times a day for about a week. Antihistaminic like Fenofexadine
180 mg can be taken once a day alongwith.
I hope this is helpful to you.