Cynthia Arce pleaded not guilty today to second-degree murder in the death of her 2 1/2-year-old daughter, Gabriella Marie Boyd.

Gabriella's father and his family looked on during the arraignment in Westchester County Court.

Arce, 29, has been in custody since April 28 when she allegedly attacked Mamaroneck police officers Osvaldo Ramos and Joseph Gaglione with knives after cops responded to her home to find a dying Gabriella.

Another officer, Matthew DiRuzza, shot Arce to end the confrontation. Efforts to resuscitate Gabriella were unsuccessful and she died at White Plains Hospital Center a short time later.

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Arce was initially charged days later with attempted aggravated murder of a police officer and arraigned in her hospital bed. She had not recovered enough to make either of her subsequent court dates in Mamaroneck in May before her lawyer agreed to have the case heard by a grand jury.

The Medical Examiner's Office eventually determined that Gabriella was the victim of a homicide. It was unable to pinpoint a cause of death and prosecutors have not revealed how they think Arce killed the girl.

Arce was indicted last week on charges of second-degree murder, attempted aggravated murder, attempted aggravated assault on a police officer and second-degree assault.

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Gabriella's death came less than 24 hours after her father, Stephen Boyd, tried to have the girl removed from Arce's care. His lawyer obtained a Family Court order granting Boyd temporary physical custody and barring Arce from any contact with the girl.

But when police went to enforce the order in the evening of April 27, Arce refused to comply, telling them Boyd had his regular visitation the following morning. Police left without seeing the girl and determined they did not have the authority to forcibly remove Gabriella from the house.

When Arce told Boyd the next morning that there would be no visit because Gabriella was sick, he tried again to get police to enforce the order but they would not, calling it a civil matter.

They finally returned to the house at 1:30 p.m. after Arce's mother called 911 to report someone was dying at the house. Gabriella was found unresponsive in her bed.

Arce's lawyer, Richard Portale, said his client cut her own throat in a suicide attempt and also tried to kill herself once police arrived. He is preparing a psychiatric defense, maintaining that Arce suffered from bipolar disorder and undiagnosed postpartum depression that could have caused a psychotic break.

Twitter: @jonbandler