A prosecutor said Thursday that the boy's father and his wife had received threatening letters.
She did not specify who made the threats.
However, defendant Manuela Maria Morgado is now prohibited from calling, texting or using any other method to contact the couple.
The judge said she'll rule later on the jail's request for a mental health evaluation.
Morgado is charged with second-degree murder.
She was arrested Monday after police found her with the body of her son, Jason Reish, in their condo.
No cause of death has been established but police are considering the possibility he was suffocated.
The boy was the subject of a custody dispute.
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