Adri Stewart, the principal of the charter high school Key West Collegiate Academy, committed suicide Wednesday by shooting herself at a gun range in Broward County, the medical examiner has ruled.

She was 30 and the single mother of three children between 1 and 13 years old.

The shooting took place Wednesday afternoon at a Pembroke Park gun range, said the sheriff's office.

Stewart later died at a nearby hospital.

Stewart left a suicide note for her family, said Keyla Concepción, a spokeswoman for the Broward County Sheriff's Office, in an email message sent Thursday evening.

An autopsy showed that the death was a suicide, Concepción said.

Stewart was named principal of the charter school, in its second year, last summer by Academica, the nonprofit company that agreed to manage the school for free.

Stewart was the third principal at the fledgling school.

Students at the charter school Thursday night were holding an impromptu candlelight vigil at the campus, said Todd German, chairman of the board of directors for Collegiate Academy.

German said, "We did what we could to notify all the parents."

Stewart, a Miami native who had a master's in guidance and counseling and a bachelor's in psychology, was finishing up a doctorate in marriage and family therapy, she said in an interview with The Citizen in August.

"I work really well in schools and I love children," said Stewart. "I combine two fields."

At age 15, Stewart got her first job as a preschool teacher. She attended Broward County community college before transferring to a four-year university.

Stewart moved to Key West in July.

In early August, she said she was excited about her new job and her career choice.

"I love students, love everything about schools," said Stewart. "School is the place they feel most comfortable, and I'm so thrilled I get to be a part of that."