REVERE – A heroin junkie was arrested Wednesday for dropping her infant niece several times on her head outside Taco Bell, police said.The aunt, Caitlin M. Powers, 21, of 118 Eutaw St., East Boston, was charged with reckless child endangerment, aggravated assault on a child, possession of heroin and disorderly conduct.Witnesses said Powers walked from a car toward the restaurant while holding the 5-month-old baby when she dropped the infant “several times,” at least once on the head, according to Police Capt. Michael Murphy.Police say it was obvious that Powers and two other people had just ingested heroin inside a nearby car. Police found heroin in possession of two of the three people in the group and said they all appeared to be under the influence.A witness, who was not part of the group, saw what was happening and grabbed the baby before police arrived, police said.Police responded to the chaotic scene at the Northgate Shopping Center on Squire Road shortly after 5 p.m. Wednesday. They found Powers sobbing nearby.A woman apparently ran toward the officers while holding the baby. She said, “Take this baby, take this baby! She keeps dropping her on her head!”A police officer held the infant and determined she was unresponsive, Murphy said.The officer reported the baby was breathing, but initially did not respond to verbal stimulus or being flicked in the foot by the officer’s finger.The baby was transported to Massachusetts General Hospital for treatment.Police say hypodermic needles, heroin, knives and stolen property were found in possession of the three people and their car.Police also arrested Anthony Paolini III, 22, of 584 Middle St., Weymouth, and charged him with receiving stolen property, identity fraud, violating the city’s knife ordinance and being knowingly present where heroin is kept.Also arrested was Jessica Lee St. Amand, 21, of 6 Middle St. Stoneham, and charged her with being knowingly present where heroin is kept, receiving stolen property and disorderly conduct.The Department of Social Services was notified about the incident.