The 17-year-old — a Cyrus super-fan —sang Justin Bieber's "Love Yourself" on Monday's episode. It was the final round of blind auditions.
Diaz' supporters have been anxiously awaiting her debut since the show launched last month.
With little performance opportunities in Cresskill, Diaz created a YouTube channel and gained fans uploading covers and originals.
In what's left of her free time, Diaz saves for college by teaching guitar lessons to children 5 to 12 years old at her Dominican Republican parents' home.
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