"Suicide's really rough to deal with as a family," Mariel told ET about losing her sister. "I mean, my father denied it. We all pretended that it didn't happen -- that it was actually an accidental overdose."
Margaux, once a top supermodel, died alone in her apartment in 1996 from an intentional overdose of pills. In 1990, she admitted her struggles to ET.
"I was drinking by myself. I was very suicidal, but I always had a smile on my face," Margaux said at the time. "I never really drank that much in public."
Mariel told ET that alcohol has been used as a crutch in her family at times, but she doesn't intend that to be the case for her or her two daughters: 27-year-old model Dree and 25-year-old model and artist Langley.
"The alcohol is self-medication for the pain that my family couldn't deal with the pain," Mariel said. "There was no conversation about stuff, so rather than having conversation, they drank. By the time I had my own children, I said the buck stops here. So when I'm parenting my girls, I'm like, 'Look, I'm not going to tell you not to drink or not to do drugs, but here 's what could happen,' because we come from a legacy that might not be as stable and balanced as somebody else's."
Mariel reveals her family struggles in her new book Out Came the Sun, which also includes details on the invite she received from Woody Allen, then 44, to accompany him on a trip to Paris when she was 18.
In the 1979 film Manhattan, Mariel played Woody's much younger girlfriend. Woody's invitation came about after Mariel had invited him to visit her in Idaho, a decision which Mariel called "naïve."
"In my mind, I'm creating this friendship -- in my stupid, naïve, young girl mind -- and then I invite him to Idaho," Mariel told ET. "It really has nothing to do with Woody. It's about me having to parent myself, and saying that's not right for me because I'm a young girl and I've never had a boyfriend before and I don't think Woody Allen's going to be my first boyfriend."
Out Came the Sun is one of two memoirs written by Mariel, as she has also released a young adult version called Invisible Girl.