The sister of a teen who died suddenly in front of about 90 of her fellow students at a Long Island high school penned an emotional tribute to her late sibling, calling her “my rock and soul.”

“God decided he needed a bright and untouched soul like yours in heaven,” wrote Emily Sparrow about her sister Maddie, 17, who became sick during marching band practice at Sachem East High School, and died Monday night.

“On behalf of Maddie I would like to say that she would want everyone to celebrate her life and be happy,” Sparrow continued in the Instagram post. “I’ll see you soon my angel.”

A medical examiner still hasn’t determined why the rising junior at Sachem North High School abruptly became sick, but some parents told CBS New York that oppressive heat played a role — though the teen seemed “fine” earlier.

“Maddie was a well loved member of her community and an amazing musician,” wrote a family friend on a GoFundMe page. “She was an inspiration to everyone she encountered. She was involved in her church and selflessly devoted her time to volunteering.”

“Everything Maddie did was so special and she touched everyone around her,” the friend added, calling the teen’s loss “unexpected” and “tragic.”

Another tragedy happened last summer at the same school, when 16-year-old Joshua Mileto died during football practice.

“It’s horrible, especially what the district suffered last year at this time,” said Suffolk County resident Barbara Staria. “It’s devastating to the families and the community. Unimaginable. I can’t even put it into words.”