A sister of Boston Marathon bombing suspect Dzhokhar Tsarnaev pleaded guilty Tuesday to misleading a police detective investigating counterfeiting.

Ailina Tsarnaeva entered the plea in South Boston Municipal Court.

The judge placed her conviction on file for 30 days, meaning that she may be sentenced to up to 2 1/2 years in jail if she gets in legal trouble during that period. Her plea also ensures that a conviction will appear on her criminal record and eliminates any appeals.

Prosecutors agreed to the deal because of the age of the case and because she has taken responsibility.

Prosecutors said Tsarnaeva had failed to cooperate in the 2010 counterfeiting investigation. They said she picked up someone who passed a counterfeit bill at a restaurant and "lied about certain salient facts during the investigation."

Her lawyer said she was not trying to protect the identity of the person who used the counterfeit money, but a third party.

Tsarnaeva, of North Bergen, New Jersey, is facing separate charges in New York, where she is accused of threatening to "put a bomb" on a perceived romantic rival.

According to a police report in the counterfeiting case, authorities were investigating the passing of a counterfeit bill by a group of people eating at an Applebee's restaurant in the South Bay Center, a mall in Boston's Dorchester neighborhood, on April 16, 2010. A server saw the group leaving and wrote down their license plate number.

Police traced the car to Tsarnaeva at her family's Cambridge home. When questioned, Tsarnaeva said she did not know the names of the people she picked up from the restaurant, according to the police report. She also told police that she had not lied but "did not want to be a snitch," according to the report.

Her brother could be sentenced to death if he's found guilty in the marathon bombing, which killed three people and injured more than 260 others. He has pleaded not guilty and is awaiting trial in January.

Federal prosecutors say Dzhokhar Tsarnaev and his older brother, Tamerlan, planted two bombs near the 2013 marathon finish line. Tamerlan Tsarnaev later was killed in a shootout with police.