At the time of her sentencing, famous family and friends spoke out in support of her.
Her mother-in-law, Ethel Kennedy, wrote in a letter that she "is a caring, nourishing mother who has nursed her four children through lifelong bouts of debilitating allergies," according to an account in Westchester's The Journal News at the time.
Kerry Kennedy, in her letter, said, "When I look at my three daughters, my wish for them is that they are as blessed as I have been to have a companion, a confidante, a friend, like Mary Richardson."
Mary Kennedy was charged later that year with driving under the influence of drugs, but that charge was dismissed in July 2011 when a judge said the evidence showed she didn't know the medications she had taken would impair her ability to drive.
There were indications her troubles started earlier. In 2007, Robert F. Kennedy Jr. drove his wife to a hospital for treatment, but she resisted and ran from the car, according to the Journal News, which cited Mount Kisco police records.
"I remember she was acting kind of out of it, kind of crazy," a witness, Rae Kesten, told The Journal News in 2007. "She was running into the street and flailing her arms around. He was trying to restrain her. I didn't know if they were fighting or not, but I was concerned."
The unexpected death of another person connected to the storied Kennedy clan brought to mind the other sorrows the famous family has suffered, including the assassinations of RFK and JFK in the 1960s.
Shopping in Bedford, Diane Glokler said, "I've always just thought that family is very tragic. They keep having tragic things happening to them. It's heart-wrenching."
Associated Press writer Verena Dobnik contributed to this report.