Gwen Tennyson (BTR)

Gwendolyn Tennyson, or simply Gwen, is a major character in Ben 10: Revamped. Though she had only a small role in the pilot episode, she is confirmed to be a main character later on.

Answers
She was with Ben and Max on a family camping trip when Ben found the Omnitrix, and warned him not to mess with it, which he later did anyway.

Trivia

 * Gwen does have powers; we just haven't seen them yet. However, the story behind them is much different than the canon version, and will be explained down the road.