I think there's a lot of debate on what counts as a "spoiler" in this show, but I think this fact was supposed to be clear at the end of episode 3 so I'll tell you: Silco adopted Powder because Vi left her. Until she said "she is not my sister anymore," he was considering killing her, but he recognized himself in her since he was betrayed by his "brother" as well (Vander), hence why he says "we will show them all". She is, outside of emotional support and the occasional successful heist, a liability to his operations.