There was still so much Sadie didn't know about the family she had been bought into. Superpowers. All seven of them had superpowers!
The odds of that happening naturally were practically nonexistent so she knew what had happened without Fletcher having to tell her. Dusk had specifically looked for kids with powers to be his henchmen.
Did they used to have families? Were there people out there missing them with no way to find them? The questions swirling in her head were incredibly depressing. As was the realization that she never would have found out about this if Fletcher hadn't called Marlee out on cheating at Crack the Egg.
As much as he said Sadie was one of them, she wasn't really. They all had a shared history she wasn't party to. They may have accepted her (even if it was begrudgingly in Lexi and Taylor's case) but there was still a wall separating them.