Sixteen-year-old Kayla Cuevas was remembered Friday as “a beautiful soul” at a packed Brentwood church about 2 miles from where police say she was beaten to death last week.

The funeral service at St. Anne’s Roman Catholic Church began with an emotional tribute from Monica Martinez, a Suffolk County legislator from Brentwood who befriended Cuevas when Martinez was assistant principal at East Middle School.

“Little by little, Kayla became my kid,” she said, her voice cracking. “I saw her grow up from that little girl . . . and turn into a beautiful young lady right before my eyes.”

Martinez called Cuevas “a beautiful soul” and “a firecracker,” known for her smile, sense of humor and high energy.

Cuevas and her best friend, Nisa Mickens, 15 — juniors at Brentwood High School’s Ross Center — were killed in what a top police official called a “brutal attack.” A law enforcement source said police believe the MS-13 street gang was involved in the double-slaying, which remains unsolved.

During the funeral, friends and relatives tightly held Cuevas’ sobbing parents, Evelyn Rodriguez and Freddy Cuevas.

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Dozens of Brentwood High students were bused in to pay their respects. Also in attendance was Suffolk County Executive Steve Bellone and Brentwood schools Superintendent Levi McIntyre.

Father Stanislaw Wadowski, a pastor at the church, told mourners in his homily that Cuevas’ death was “a voluntary act of violence.”

“It was a crime. It was a life that was broken,” he said. “It was a child — a person who parents love. She was their life; she was their everything.”

Wadowski said children in gang-plagued Brentwood lack “safe havens” and can’t do something as simple as putting up a basketball hoop without worrying about the consequences.

“We failed to protect . . . Kayla and Nisa, and probably other children,” he said.

Outside, security was stepped up. Police patrolled the area in marked vehicles. Members of the Guardian Angels stood watch by the church’s front doors.

Clutching a strand of crystal rosary beads, Rebecca Vansickle, 72, sobbed as she watched pallbearers carry out Cuevas’ coffin.

“I don’t even know these girls and I can’t stop crying,” said Vansickle, who came to pray for the slain girls. “This just breaks my heart. This shouldn’t have happened to them. They were so young.”

Bellone offered his condolences to the family as they climbed into waiting limousines. After the service, Bellone tried to muster words to describe the family’s pain.

“They’re devastated,” Bellone said of Cuevas’ family. “They’re just trying to deal with it all but it’s hard. One thing they expressed to me is that they want something positive to come out of this.”

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Cuevas was buried at Queen of All Saints Cemetery in Central Islip.