Hi,
Skin irritation could be due to various reasons. Thorough history is needed. You Ve not mentioned clearly the type of rash she develops. It could be chronic urticaria or xerotic dermatitis or chronic eczema. Consult a dermatologist for a proper diagnosis and treatment.
Health Tips
Use a moisturizing soap for her bath and moisturize her skin regularly at least twice in a day. Moisturization can decrease itching to a great extent.