Sherlock's Sister (BBC)

Ebony Holmes was always considered the normal one. She couldn't deduce people like her elder brothers could, and she was definitely not sociopathic. She was normal. Ungifted. What her family doesn't know is that she'd always been able to deduce. After seeing how Mycroft and Sherlock were treated at school, she vowed never to use her gift. She soon learns how difficult it would be to fool her family and everyone around her

Sherlock belongs to BBC. All of the characters belong to BBC except for Ebony. Suggestions are welcome but there's no garuntee ill use yours.