Amy, who hails from Malta, appeared on the ITV show on Saturday, stunning the judges with a performance of Nella Fantasia.
Her powerful soprano voice came as a surprise to the judges - as she was very nervous taking to the stage.
"We didn't think you'd be able to talk, let alone sing, and you genuinely filled the room," said Simon. "It was glorious."
David Walliams added that the audition was "like watching a caterpillar turn in to a butterfly".
However, it was not the first time Amy had taken part in a major talent content.
In 2015, she was one of twenty candidates who competed to represent Malta in the Junior Eurovision Song Contest, although she ultimately failed to make the cut.
Amy has now admitted that she found meeting Simon more terrifying, telling the Metro that BGT is "a lot bigger" than her Eurovision attempt.
"I wasn’t that nervous, as it wasn’t that big of an audience," she said. "But with Simon, I was just a little bit more nervous."
The 16-year-old eventually lost the Eurovision slot to Destiny Chukunyere, who's also a familiar face to BGT viewers.
Destiny took part in the show last year and reached the semi-final, though failed to make the grand final.
Meanwhile, Amy give a little hint about her future plans for BGT, suggesting that she'll be sticking to classical music.
"I’ve never sung pop before," she revealed. "I was in musicals as a kid and then it developed into opera."
Amy got four yesses, making it on to the judges' shortlist - though we're yet to find out whether she'd made the live shows.
For now, the Britain's Got Talent 2018 auditions continue on Saturday nights on ITV.