Jebina Yasmin Islam said there were still “not enough words” to describe the pain of her sister’s death.
Ms Nessa was attacked as she walked through Cator Park in Kidbrooke south-east London, on her way to meet a friend on September 17.
We need to make sure that this does not happen again and Boris, Sadiq Khan, they need to step up
Jebina Yasmin Islam, sister of Sabina Nessa
Her body was discovered nearly 24 hours later covered with leaves near a community centre in the park.
Ms Nessa’s family organised a celebration at the weekend to mark what would have been her 29th birthday.
Speaking to ITV news, Ms Islam said women should not have to be restricted by fear of walking home alone.
“Boris (Johnson) needs to do something, Sadiq Khan needs to implement something for us to feel safe to walk the streets alone,” she said.
“We shouldn’t be going home extra early just because we don’t feel safe.
“We are independent, we live in a country where we can walk alone but we can’t because of what’s happening, what happened to my sister, what has happened in the past.
“We need to make sure that this does not happen again and Boris, Sadiq Khan, they need to step up.”
Garage worker Koci Selamaj 36, from Eastbourne, who is charged with Ms Nessa’s murder, is due to appear in court on December 16 for a plea hearing.
Describing the aftermath of her sister’s death, Ms Islam said: “You don’t feel like this would happen to you… there aren’t enough words to explain how much it’s hurting inside.
“The world is carrying on. Who would have thought it was five weeks on that she’s passed away?
“It feels like we got the news yesterday.”
Shortly after the incident, almost 200 people gathered for a vigil in Eastbourne to honour the memory of Ms Nessa.
“We’re four sisters, we’re not three,” said Ms Islam.
“We’ll always be four sisters even though she’s not here.”