Parkland shooting survivor Sydney Aiello, 19, died Sunday after committing suicide, according to police.

Aiello was reportedly suffering from “survivor’s guilt” on account of one of her very close friends being killed in the mass school shooting last winter, CBS 4 Miami reports.

Cara Aiello, Sydney’s mother, told CBS 4 that Sydney had also been diagnosed with post-traumatic stress disorder, making it difficult for her to attend her college classes because of her fear of being in a classroom. She said Sydney was frequently sad but never reached out for help before killing herself. (RELATED: Here’s The Wounded Warrior’s Response To David Hogg That Is Going Viral)

Sydney’s close friend, Meadow Pollack, was one of the 17 victims of the shooting last winter.

Meadow’s brother, Hunter Pollack, tweeted Wednesday in response to Sydney’s suicide, urging Twitter users to help the Aiello family by contributing for the funeral expenses: “Beautiful Sydney with such a bright future was taken from us way too soon. My friend’s sister and someone dear to Meadow.”

Beautiful Sydney with such a bright future was taken from us way too soon. My friend’s sister and someone dear to Meadow. Any help for the family to cover funeral expenses would be appreciated. Please RT and donate! https://t.co/3eg2Su4Jbv — Hunter Pollack (@PollackHunter) March 21, 2019

Ryan Petty, father of Alaina Perry — another one of the 17 students killed in the Parkland shooting — told CBS 4 Thursday, “It breaks my heart that we’ve lost yet another student from Stoneman Douglas.” (RELATED: Parkland Students’ Anti-NRA Protest Against Publix Backfires)

“Some of the questions that need to be asked are: Do you wish you were dead and not wake up? Second question: Have you had thoughts of killing herself?” he said. “My advice to parents is to ask questions. Don’t be afraid. Don’t wait.”