How could we have protected you?

At 25, my niece admitted to me that my adult brother had touched her inappropriately. He was heartbroken from the divorce with her Mom and an undiagnosed bi-polar alcoholic/drug addict. She experienced unwanted touching at 9 from a girlfriend's sons that should not have been allowed. She didn't know what was happening & was confused. Telling me was intended for me to share with his therapist so that his guilt/addiction would be interrupted and he could heal. She forgave him. He'll probably never forgive himself. Her wish is that he'll become sober, healthy and enjoy being with her young family, which is whole and beautiful. That's why she shared her story. She's so brave and strong. She is wisely excluding him until he is whole. With a family scattered all over the country and an isolation that my brother forced, how could we have better protected her? This will always haunt me.