Her grandparents now live in metro Atlanta, and her mother is a 1991 graduate of Marietta High School.
Trump is addressing the nation a day after the shooting that killed at least 17 people.
Meanwhile, a GoFundMe page has been set up for Maddy to help her family pay for medical expenses.
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Police and deputies were seen surrounding the school with their guns drawn as they guided students outside of the school to safety.
In the wake of the shooting, students said they were not surprised that Cruz had been implicated.
He said authorities told him it was some kind of explosive at one of the residences. "No child, teacher or anyone else should ever feel unsafe in an American school", he wrote.
"I think we spoke with you in the past about a complaint that you made about someone making a comment on your YouTube channel", the agent said in the message, which Bennight provided to BuzzFeed News.
Trump said he has spoken with Florida Gov. Rick Scott about the shooting.
US President Donald Trump offered his condolences to the families of the victims. He had been expelled from the school previous year for disciplinary reasons.
Online, the shooting renewed calls for stricter gun control in the country.