"When we found out she was last seen in Toolern Vale, each weekend we would meet in Bacchus Marsh and drive between Toolern Vale and Mount Macedon...we actually went everywhere looking for her.
"Water catchments, hillsides, mountains, but we really didn't believe she had just been left without being covered.
"In Macedon, my sister said 'I can smell something' and I said, don't worry, it's probably just a kangaroo.
"Later on, we found that's where was found."
Sam said she felt compelled to speak out because "no one was being a voice for Karen".
She also said Borce was a "controlling" husband who "controlled how Karen died, controlled where she went and that her body wasn't looked after".
"Now he is controlling that he is able to have a lighter sentence which I find incredibly unfair," Sam added.
The interview comes hours before Mr Ristevski is due to be sentenced for his wife's death at Victoria's Supreme Court.
He pleaded guilty to manslaughter in March after repeatedly denying involvement in Karen's killing.