In a statement to the Associated Press, Kidder's daughter Maggie McGuane said the family decided to make her mother's suicide public because "it's important to be open and honest about the suicide so there's no cloud of shame".
The Park County, Montana coroner's office has ruled Margot Kidder's death a suicide.
She starred in the Superman trilogy released between 1978-1983 as hotshot reporter Lane, who was also the love interest of Clark Kent - played by Christopher Reeve, who died in 2004. The Canadian-born actress had always been open about drug and alcohol addictions, which she said partially triggered her very public breakdown in 1996.
McGuane stated she knew her mother's death was a suicide when taken to the home.
In 1996, she was briefly homeless during her struggle and she became a very public advocate for mental health. A cause of death was not originally reported, but Kidder's manager, Camilla Fluxman Pines, said at the time that she had passed away peacefully in her sleep. She's also an activist for many causes.
Regarding her family life, Kidder got married three different times throughout her life and has one daughter, Maggie McGuane.
"It's a very unique sort of grief and pain".
McGuane, who could not immediately be reached for comment Wednesday night, told the AP that she urged people with mental illness to seek help.
In what was an obvious reference to the Superman movies, Kidder made a cameo in Smallville along with the series' stars Michael Rosenbaum and Allison Mack.
The actress died at the age of 69 at her home in Livingston, Montana, on 13 May. She wants to avoid any "cloud of shame".
She later appeared in small films and television shows until 2017, including RL Stine's The Haunting Hour.