Saffo had helped her sister get in-patient hospitalization treatments "several times in the past 3-4 years", she wrote to the Missouri newspaper.
A statement from the family via in NY spokeswoman on Tuesday had said: "We are all devastated by today's tragedy".
Kate Spade had no alcohol, business or substance abuse problems, he said.
"There was a moment when you couldn't walk a block in NY without seeing one of her bags, which were just like her; colourful and unpretentious", Wintour said in a statement.
He said her death was a "complete shock". He said they were not legally separated and never discussed divorce.
"I, personally - I don't know about Andy - took off a good 9 years raising my daughter, and absolutely adored every moment of it", said Spade.
In addition, a spokesperson for the Office of the Chief Medical Examiner confirmed the death of Spade, also known as Katherine Brosnahan, and accepted her case.
Over the years, Brosnahan and Spade appeared together on red carpets and other events as the actress' star rose.
It is thought that in a suicide left for her 13 year old daughter Frances, Kate told her to "ask daddy".
Andy Spade, the husband of Kate Spade, has released a statement following the designer's death.
The sister said she tried to get help for Spade in a mental health facility. "They loved each other very much". Her brother-in-law, actor David Spade, tweeted a picture of her a book signing and he said 'I love this pic of her, so pretty. "Please!'", Saffo said. "I know she perhaps had a plan, but she insisted she did not". "My daughter and I are devastated by her loss, and can't even begin to fathom life without her", he writes.
"Kate and I during Christmas family photos".
An unnamed source close to the family told People Magazine that other members of the clan are upset over Saffo's comments, and calling into question how close Saffo had been with her sister in recent years. The National Suicide Prevention Lifeline (1-800-273-8255) provides 24/7, free, confidential support for people in distress, as well as best practices for professionals and resources to aid in prevention and crisis situations.