Chad Lowe’s oldest daughter, Mabel, is remembering her 13-year-old sister Fiona with a heartbreaking promise: She will keep her memory alive.

Mabel, 17, shared a series of photos of the sisters on Instagram over the weekend, including childhood moments together and images reflecting Fiona’s love of dance.

“I love you so much, Fiona,” Mabel wrote. “I wish your short time here was easier and I hope your mind is at ease now.”

“I will honor you forever and keep your memory alive,” she continued. “I love you, I hope you knew just how much.”

Fiona died at a Los Angeles hospital on Sept. 29, according to the County of Los Angeles Medical Examiner. She was 13. The medical examiner later ruled her death a suicide.

Chad Lowe and his wife, Kim Painter, announced their daughter’s death in a statement describing the devastating loss their family is facing.

“We are deeply heartbroken by the loss of our beloved Fiona,” the family said.

They remembered Fiona as “a loving young girl who was smart, creative and loved to dance.”

“She was adored by her sisters and she was deeply loved by her parents,” the family said. “In fact, she was the light of our lives.”

Fiona was the middle of Lowe and Painter’s three daughters, between Mabel and younger sister Nixie, 10.

Those who knew Fiona have also shared memories of a gentle, artistic teenager whose passion for dance was a major part of her life.

“Fiona was sweet, quiet and kind,” a source familiar with her school community told PEOPLE. “Dance was her biggest passion. She had a very artistic soul.”

The source said Fiona was “always kind to other students” and described her death as devastating for a close-knit school community where many parents and families know one another.

Support has also poured in for Mabel and the Lowe family. Jeremy Renner offered his “deepest condolences,” while Jessica Capshaw told Mabel she had been keeping the family in her “thoughts and prayers.” Kimberly Williams-Paisley also sent “prayers and so much love.”

Lowe, the younger brother of actor Rob Lowe, is an Emmy-winning actor and director known for roles in “Life Goes On,” “Pretty Little Liars” and “9-1-1: Lone Star.” He and Painter have largely raised their three daughters away from the Hollywood spotlight.

Rob Lowe and other family members and friends have rallied around Chad and Painter in the days since Fiona’s death, according to PEOPLE.

“Everyone’s heartbroken,” a source said. “Right now, the focus is on being there for them in any way they can.”

In their statement, Fiona’s family asked for prayers and privacy as they grieve while also urging others who may be struggling to seek help.