Stephanie Kercher made the comments in a documentary about Amanda Knox, who was reconvicted of murdering the 21-year-old in the Italian town of Perugia in 2007 last month following a second trial.
Only one person - Rudy Hermann Guede - is currently behind bars for her murder after American Knox and her former boyfriend, Italian Raffaele Sollecito, successfully appealed against their original guilty verdicts. Afterwards, Knox returned home to America and has so far refused to go back to Italy to serve her jail term following her second conviction, saying she will only be extradited "kicking and screaming".
Ms Kercher told the BBC Three documentary Is Amanda Knox Guilty? that her sister did not deserve what happened to her.
"Everything that Meredith must have felt that night. Everything she went through. The fear and the terror and not knowing why. She didn't deserve that. No one deserves that," she said.
"We all definitely want some sort of closure."