In an email to CBS News, Spade's sister Reta Saffo said she believed the designer suffered from bipolar disorder.
"It finally took its toll on her. A very tragic and sad ending to the life of a very colorful and delightful being," Saffo wrote, adding that she "tried numerous times to get her help."
Saffo further discussed her sister with the Kansas City Star, saying in an email that Spade's suicide was "not unexpected by me."
"Sometimes you simply cannot SAVE people from themselves!" she wrote, saying that her family had attempted to help Spade, but the designer believed hospitalization might tarnish the "happy-go-lucky" Kate Spade brand.
Saffo wrote that Spade was "always a very excitable little girl and I felt all the stress/pressure of her brand (KS) may have flipped the switch where she eventually became full-on manic depressive."
She continued, "I'd come so VERY close to getting her to go in for treatment (to the same place Catherine Zeta-Jones went for her successful bipolar treatment program). I'd spoken with them on the phone (not telling them exactly who the patient would be). They agreed to fly in and talk with her and take her with them to the treatment center."
"She was all set to go — but then chickened out by morning. I even said I (would) go with her and be a 'patient' too (she liked that idea) I said we could talk about it all — our childhood, etc. That I could help her fill in any blanks she might have."
Saffo wrote that the pair would get "close" to packing Spade's bags, but in the end, the thought of her brand's image was "more important" for her.
"She was definitely worried about what people would say if they found out," Saffo wrote.
Saffo also shared some of Spade's last words to her, in which the late designer discussed her funeral.
"One of the last things she said to me was, 'Reta, I know you hate funerals and don't attend them, but for me would you PLEASE come to MINE, at least. Please!'" she wrote. "I know she perhaps had a plan, but she insisted she did not."
After her passing, Spade's family said in a statement, "We are all devastated...we loved Kate dearly and will miss her terribly."
If you or someone you know needs help, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).
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