(CBS) A New York City landlord is demanding more than $27,000 from the estate of a Sept. 11 terrorist attack victim.

Danielle Kousoulis, 29, worked on the 104th floor of the World Trade Center's north tower as a vice president for Cantor Fitzgerald. She signed a lease on a $2,500-a-month loft apartment 10 days before a hijacked plane crashed into her workplace.

In a letter this month, landlord Denise M. Lyman claimed she was an unpaid creditor and threatened to take Kousoulis' family in Haddon Township, N.J., to court.

The New York Daily News reported that one of the complaints against the dead woman was that she failed to give three-months notice that she was leaving.

"We're going through enough without having to go through this as well," Danielle's mother, Zoe, told the Courier-Post newspaper of Cherry Hill, N.J. "I can't see how greedy people can be."

Zoe Kousoulis, the administrator of her daughter's estate, said there have been other problems with Lyman.

She said Lyman refused to let the family into their daughter's apartment to get a hairbrush for a DNA sample to identify any remains. The family finally obtained the sample with the assistance of the police.

Lyman did not return messages from The Associated Press seeking comment.

In letter to Lyman from Zoe Kousoulis last October, she told the landlord that her daughter's apartment would be vacated by Oct. 22. Family members said they cleaned the apartment, left the key with the doorman and arranged for the Salvation Army to take away remaining furniture.

When Lyman received the letter, she called Danielle's brother-in-law, Sean Hagerty, and demanded that nothing be removed from the apartment, the Kousoulises said. The landlord also told the doorman not to allow the Salvation Army into the apartment.

Neighbors and a doorman said Lyman and her teenage daughter moved into the apartment in the Packard Condominium building.

Under New York state common law, a lease does not automatically end when a tenant dies — both parties must agree to surrender it. But New York City attorneys and property managers said a landlord moving into an apartment is evidence of a surrender.

"If the landlord decided to move into it, then she would have extinguished the responsibility of the tenant," said Charles Mehlman, senior vice president of the Lefrak Organization, which owns and leases 60,000 apartments in the city.

Attorney Jack Lester, who specializes in real estate law but is not involved in the Kousoulis case, also said the family was under no obligation to pay rent beyond the point the landlord moved in.

"I think it's outrageous from a legal standpoint, and it's even worse from a moral and humane standpoint," Lester said. "It's shocking that she would have no regard for the survivors of the people that perished in the worst attack on American soil."

A New York City attorney is handling the Kousoulises' case pro bono. The American Red Cross also offered financial assistance.