Your daughter might be having intertrigo
or seborrheic dermatitis
. The confirmed diagnosis can only be delivered after a thorough visual inspection of the lesion. However to offer empirical treatment, you can clean the affected area with warm saline water and apply a combination anti fungal, antibacterial and steroid
cream like monovate gm cream twice in a day for a week to see response. Hope that solves your query. Take care.