LYNN – A Hanover Street woman pleaded not guilty Friday to charges she inflicted a serious head injury on a 4-month-old boy in her care.Prosecutors said the boy sustained a brain injury sometime between mid and late November. Judge Ellen Flatley ordered Bessy Mira, 27, 53 Hanover St., Lynn, held on $2,500 bail and ordered her to surrender her El Salvadoran passport.The boy is expected to survive the injury.After reviewing evidence and interviews with Mira, the boy’s parents, doctors and social workers, police arrested Mira Thursday night and charged her with assault and battery on a child causing substantial bodily injury.A document filed in District Court Friday stated a hospital diagnosis of the boy’s injury “indicates subdural bleeding and retinal bleeding indicating ‘shaken baby syndrome.'”Police and social workers started investigating Osmer Perez-Morales’ injuries on Nov. 28 after Mira asked a neighbor to call for help and emergency workers transported the boy to Salem Hospital’s emergency room and then to Massachusetts General Hospital.A Department of Social Services investigator said Mira told her that after the boy’s mother dropped him off at her apartment, she let the baby sleep in his car seat in her 2-year-old son’s room while she showered.”She came out of the shower and noticed that the baby was sweating and that his eyes rolled back in his head,” investigator Elise Woiszwillo wrote in her report.The boy’s mother told a doctor she noticed bruising on her son’s cheeks 15 days earlier when she picked him up at Mira’s home. She called Mira who, according to the Social Services report, said another child in her care could have caused the bruising by “touching the baby and kissing his face.”A doctor who examined Perez-Morales on Nov. 28 also noticed earlier indications of bleeding in the boy’s brain.Woiszwillo filed a care and protection order in Boston Juvenile Court on the boy’s behalf on Nov. 30 and the judge presiding at the court hearing allowed the boy’s parents to retain custody of him.Massachusetts General discharged the baby on Dec. 1. Lynn Lt. Marie Hanlon interviewed an MGH care and protection physician three days later who told her the baby had sustained a brain injury and probably faces learning disabilities, vision problems and behavioral issues during his school years.Dr. Alice Newton told Hanlon she could not pinpoint the exact time when the injuries occurred, but said, “I would be very concerned that this happened sometime after the baby was dropped off (at the daycare) because of the fact that the baby appeared well prior to this.”Patrick Callahan, Mira’s attorney, said the inability to pinpoint when the injuries occurred is “extremely significant.””She wants to prove she did not do this,” Callahan said.