Plimpton died Tuesday from a brain aneurysm at the age of 59.
"Laura worked for me and the company for more than 25 years," Stewart wrote. "For the past several years Laura edited, researched, and often wrote, captioned, and photographed content for this blog and The Daily Wag."
Stewart shared her earliest memories of Plimpton, including the birth of the youngest of the six Kostyra siblings.
"Our mother wanted to name her Dorothy, but we persuaded her to name her Laura instead," she wrote. "We still don't know why we didn't like the name Dorothy, but Laura was beloved by all as Laura."
— AOL.com (@AOL) August 7, 2014
Nothing could have prepared Plimpton's family for the loss they would face this week.
According to Stewart's blog, Plimpton began her day at 5:30 a.m. as usual on Tuesday and "did her one hour of elliptical and treadmill, then showered and felt ill enough to call her husband Randy for help." Her husband took her to Norwalk Hospital in Connecticut, but there was nothing to be done for Stewarts younger sister. Doctors at the hospital determined "she had suffered a massive brain aneurysm."
"Laura left a living will so she was kept on life support until today so her three children could say their goodbyes, and the testing could be completed for organ donation," Stewart wrote. "We are so sad but also happy that Laura had the foresight to donate so many healthy organs to needy people."
— Us Weekly (@usweekly) August 6, 2014
Plimpton leaves behind her husband, Randy; her three children, Christopher Herbert, Sophie Herbert Slater, and Charlie Plimpton; and her two children-in-law, Tim Long and Dan Slater.
Stewart ended her blog post with a request for readers to keep the family in their thoughts.
Following her first husband's death, Plimpton began working with her sister. She ran the company's daily operations at Martha Stewart Living Omnimedia for more than 25 years.
Image via YouTube