We spoke to Isabelle Tate‘s agent, who tells us Tate passed away peacefully in her sleep.

We’re told Isabelle suffered from Charcot-Marie-Tooth, a rare progressive neuromuscular disease which confined her to a wheelchair. Her agent says the disease affects the legs but can also affect internal organs such as the lungs and heart. Because of the disease, Tate had basically given up on her dream of acting … until she got the 9-1-1 role — her first big booking which was just perfect for her.

Tate’s funeral will take place Friday.

Tragedy has rocked the “9-1-1: Nashville” … one of the show’s young actresses, Isabelle Tate, di3d shortly after filming an episode.

According to her obituary, the rising star di3d Sunday at age 23. Her agency, McCray Agency, confirmed the heartbreaking news … though her cause of death has not been disclosed.

Isabelle played Julie in the pilot of ABC’s newest “9-1-1” spinoff, starring LeAnn Rimes, Chris O’Donnell, and more. Before breaking into acting, she graduated from Middle Tennessee State University.

Friends and family are remembering her online as “full of fire,” “a fighter,” and “the most caring, loving person.”