As your girl hits puberty, her hair will likely start to get oily. This is new to her and she needs your gentle guidance!
With the onset of puberty and hormones starting to pump through a body that is ready to start changing, oil glands start over-producing. This is what can cause acne and also - greasy hair.
How often do should she scrub?
You may need to experiment a bit. If your girl is active in sports and sweating, she should wash her scalp everyday. Others do better with washing their hair every other day or even every third day.
Greasy hair is the result of overactive sebaceous glands, which are producing too much sebum. Although sebum is good for the hair, keeping it healthy, smooth and preventing it from drying out and breaking, too much can cause the hair to look slick and greasy.
You may need to revisit how to scrub your hair with shampoo in the shower or tub. Encourage your girl to pay extra attention to the crown area that can sometimes get missed if she has long hair.
Empowering her to have healthy hair:
Let her pick out a shampoo and conditioner at the store.
I know it is easy just to give her some shampoo and tell her to scrub it. However, if you want her to get excited and take some ownership over her haircare, it is a super easy and fun mother-daughter moment to let her pick out her own scent. Be sure to take notice of clean, shiny hair that smells good, and comment on it. It will make her feel good that you noticed and also reinforce that is good hair care.