Hudson, 29, has repeatedly declined to talk publicly about the shooting deaths of her mother, brother and nephew in October 2008, but in an interview with Winfrey, she said she was still trying to make her mom proud.
"I try to do everything to say, 'OK, will my mother like this? Will she be pleased? How do I know she's happy and she's smiling down at me from heaven?"' Hudson said.
Shedding tears, Hudson said she could hear the voices of her brother and mother telling her to "knock it off," stop crying and keep going.
The estranged husband of Jennifer Hudson's sister, Julia, is charged with first-degree murder in the killings.
The Grammy and Oscar winner has been a spokeswoman for Weight Watchers and said the program has helped her drop from a size 16 to a size 6.
"It's like a brand new me," Hudson said. "Sometimes I don't even recognize myself."
Winfrey announced on her show that the audience would get three free one-year memberships to Weight Watchers so they could sign up with two friends.
The Associated Press contributed to this story.