My daughter is 13 years old and she started having...

What is the treatment of acne in an adolescent ?
Don't scratch the acne
Wash face with warm water then cold water
Drink large amounts of water
Eating vegetables and fruits they contain antioxidants that protect the skin.
Moisturizing Creams.
steam bath.
Honey mask.
Stay away from foods that contain fatty substances such as fast food and chocolate
Use vit A derivative Isoterntoin creams , but whith extreme caution due to its bad effect on pregnancy and liver
Use microdermabrasion
Use benzoyl peroxide
Use sulfur soap or antiseptic soap
Do not put makeup or put perfume on the face because this fragrance contains alcohol which increases the secretion of fat cells.
 peeling the skin with peeling creams such as fruit acids that help acne peel off, it may be useful.
Or by laser and this process is done by directing specific waves of light on the skin to peel layer after layer through evaporation of damaged cells and remove the effects that resulted from acne
What is my advice to you ?
I advice you to visit a dermatologist to determine the severity of acne and the appropriate medicine for her

You are, welcome 
Kind regards