A woman accused of stabbing two young nieces at their home across from Martha Stewart's estate north of New York City told police she didn't know why she did it, according to court papers filed Tuesday.

Lisa Turkki, 40, of East Syracuse, was arraigned Tuesday on an attempted-murder indictment. She is accused of using kitchen knives to slash Maeve Kelly, 7, and Annabel Kelly, 9, of Katonah, while she was baby-sitting them July 31.

Turkki pleaded not guilty. Her attorney, Jeanne Mettler, said she plans to pursue a psychiatric defense.

"My client has struggled with mental illness for all of her adult life," Mettler said. "This is a very sad case, but we're hoping it can be resolved in a way that is just and humane."

If convicted, Turkki could be sentenced to 25 years in prison.

Police said the girls were conscious and talking when they were found, and they have recovered from their wounds.

Along with the indictment, Westchester County prosecutors filed several statements Turkki allegedly made to police at the house and at police headquarters on the night of the stabbings.

They say Turkki told police more than once that she stabbed them. She said she didn't know why but that she had driven to her sister's home to kill her family, though she also said, "I feel sorry for what I did to my sister."

Turkki said she was "schizoaffective" and may have missed some medications, the papers say. A person with schizoaffective disorder can have hallucinations, delusions, mania and depression.

The girls' parents, Joseph and Eva Kelly, were at a concert at the Caramoor Center, a popular summertime music venue within walking distance of their house, when the girls were stabbed.

Turkki herself called 911, the papers say.

Besides two counts of attempted murder, the indictment alleges assault and weapon possession.