How do I stop my daughter's hair breakage caused by early puberty?

I have been growing my African-American daughter's hair since she was a baby. Her hair has always been long and healthy. Now, at age 9, she is beginning early puberty and her hair is breaking off. She has lost about 2.5 inches of hair within the last year. I keep her hair moisturized, oiled with good products, trimmed, and natural without applying much heat and no chemicals. I've even had her hair braided in cornrows and large individuals to help protect it. She takes vitamins, probiotics, and eats healthy. Nothing seems to work to stop the breakage. Are there any supplements that can be taken during puberty to help stop hair breakage? Are there any other recommended suggestions? Thanks!