How Can I Cultivate a Sense of Identity Instead of Being a Shadow of Her Older Brother?

My older child is high energy seeking has required a lot of attention the whole house walked on eggshells with his moods and outbursts from age five to eight. So now at age nine, his younger sister has learned from a young age to observe and keep things calm and safe. How can I cultivate her sense of self and own interest instead of being a shadow of of older brother overcome concern of her codependency foundation? And you read the question one more time was something about identity how can I.