Back in August, Chabert wrote of her sisters, "Couldn't let #nationalsistersday pass without saying how much I love my two sisters.
"They are the best big sisters ever and I thank God for them every day. Love you, Wendy and Crissy."
The well-loved actress was sent condolences from several of her celebrity friends, including Mean Girls co-star Daniel Franzese, known for playing Damian.
"Oh Lacey! so sorry. Praying for you and your family," he wrote.
Several other 90s child stars reached out to share their well wishes with Chabert.
Former Full House star Candace Cameron Bure wrote "Lacey, we are praying for you, your family and Wendy's family. We love you, always here for you my sweet sweet friend."
Sabrina the Teenage Witch's Melissa Joan Hart wrote that she was "devastated and heartbroken! I am so sorry Lacey! Sending you so much love!"
Danica McKellar, known for playing Winnie Cooper in The Wonder Years, wrote, "Oh my goodness, Lacey. I love you so much and am sending prayers and love to you. I don't know what I could possibly do but please call on me if I can do anything at all."
Chabert got married to her boyfriend of several years David Nehdar in 2013. The couple welcomed a daughter named Julia in September 2016.
Fans were delighted when the Mean Girls cast reunited last year to recreate one of the film's most iconic scenes.
Lindsay Lohan shared the clip to her millions of followers as she and her co-stars filmed their parts from their homes.
