Korshunova, 20, was found dead June 28 following a fall from a Manhattan building.
Her friends and mother, Valentina Kutenkova, told the New York Daily News they think police failed to properly investigate her death and were too quick to call it a suicide.
The Kazakh model's friends and mother also said they were told the building next door wasn't investigated, even though police said they thought it was possible Korshunova jumped from there and not her own balcony.
"Maybe there was someone else there ... I want to know what really happened," Kutenkova told the Daily News. "She didn't have a single reason to do this and 1,001 reasons to live."
But the NYPD told the Daily News both buildings were looked at.
"We can appreciate how painful this must be for any family member but a mother in particular," Deputy Police Commissioner Paul Browne told the newspaper. "Detectives ... followed all the best investigative leads to their proper conclusion."