The former Glee star's new CBS drama will debut this fall, but approximately 400 moms and daughters were treated to a sneak peek screening of the show's premiere episode late last month.
In a video debuting exclusively on PEOPLE, Benoist surprises the unsuspecting fans by appearing on stage following the screening.
"I was beside myself," Benoist tells PEOPLE of meeting her young fans. "There was an electric energy in the air that day. It was pure excitement."
Benoist says she's still hasn't "quite absorbed" the impact her strong heroine can have on her new, young fans.
"In some ways it has hit me, and in other ways it hasn't," she says. "I am fully aware of how much Supergirl means to her fans and how much she has the ability to affect people for the better, but I'm not sure I am quite aware of how large that circle of affectation is – and I might not be until the show begins to air in the fall."
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Supergirl is slated to premiere Oct. 26 on CBS.