Nora West-Allen and Black Streak

Nora didn't come to the past alone. She has her older-twin brother with her, her boyfriend, and her best-friend. But are they part of her mistake? Did she freelance? And who is this Black Streak that they keep talking about? All that is clear is that BS is a speedster but is BS good or bad? And who the hell is this woman that keeps appearing asking for their aid?