Sophie and Alex knew each other vaguely in middle school. They weren't that close, until after the bug bite in the final weeks. Sophie was there during the camping trip and events when Alex gained her powers (and a participant). As time went on Sophie saw the hints and uncovered that Alex was now super, just before the semester ended.
When meeting in costume by happenstance Britany Kale asked her hero identity and Alex awkwardly refused.
Influence:
Sophie Waters and Britany Kale have influence over Alex.
Alex has influence over Adam Meyers