Thirty-one-year-old Julie Tejeda was held without bail Thursday following a court apperance on charges including assault with intent to murder.
The judge ordered the evaluation after Tejeda was examined by the court's mental health clinician.
Officials said the ambulance was transporting an "emotionally disturbed" patient to a hospital Wednesday when the responder was attacked.
The EMT, whose name has not been released, is expected to recover from her wounds.
Prosecutors said Tejeda also used pepper spray against the stabbing victim and a second responder in the ambulance.
Suffolk District Attorney Rachel Rollins says quick action by that other EMT likely saved his colleague's life.
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