On a hot February afternoon, 30 or so teenage girls sit quietly in a small classroom. For a brief time, they’re shielded from the bustle of Kibera, a sprawling neighborhood in Kenya’s capital of Nairobi. At the back of the crowded room, a young girl holds a toddler, her gaze flicking between the child and a row of bright red and black helmets lined up on an old table at the front like Roman galea. Beside the table stand members of the Inked Sisterhood. One wears a shirt that declares,…