Martha Stewart (left) and Laura Plimpton
08/06/2014 AT 11:15 AM EDT
Martha Stewart's younger sister, Laura Plimpton, died Tuesday from a brain aneurysm at her home in the Weston area of Connecticut, PEOPLE has confirmed. She was 59.
"My youngest sister, and the youngest of the six Kostyra siblings, Laura Kostyra Plimpton, passed away today in Norwalk Hospital," Stewart, 73, announced in a tribute posted to her website
Although Plimpton was rushed to the hospital after falling ill, doctors could not save her, Stewart's message said.
"She woke up Monday morning at 5:30 a.m., did her elliptical and treadmill, then showered and felt ill enough to call her husband, Randy, for help," she writes.
"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."
Following her first husband's death, Plimpton went to work for her sister's expanding empire and more than 25 years later still ran the company's daily operations at Martha Stewart Living Omnimedia.
"We are so sad, but also happy that Laura had the foresight to donate so many healthy organs to needy people," Stewart writes. "Laura deserves the very best; she was an extraordinary mother, wife, and sister."
(A previous version of the post also called Laura an extraordinary "employee.")
In a 2004 interview
with Larry King
, Plimpton described the "special relationship" she shared with Stewart.
"I was 5 when she got married, and all I wanted to do was be around her, her husband, and then when Alexis was born, I just wanted to take care of Alexis," Plimpton said. "She was a mother figure in many ways, a teacher, an employer."