Sherri is definitely not the kind of person who would hero on her own (though she would be a hero, rather than a villain), and would have to be a part of a team. She'd have been living a quiet, unobtrusive life, until someone noticed that when she told a story, she could keep an entire room under her spell. That, combined with the fact that she has an abundant amount of knowledge packed into her little skull, and knows how to find something out even if she doesn't already know it, would make her a valuable addition. Either a team of villains would try to nab her for their uses and the heroes would rescue her and take her in themselves or, much more likely, the heroes would notice and approach her and she'd find her place as quietly and unobtrusively as she does everything else.