NEW YORK — The troubled Brooklyn woman accused of drowning her three children in the ocean off Coney Island was arraigned on murder charges Friday. A judge ordered Erin Merdy, 30, held without bail during the brief arraignment at NYU Langone-Brooklyn, where she’d been undergoing a psychiatric evaluation. Merdy allegedly drowned her children, 7-year-old Zachary, 4-year-old Liliana and 3-month-old Oliver in the surf in the wee hours on Monday morning. Her eyes closed, Merdy whispered her responses to the judge’s question as she leaned over in her bed dressed in a yellow hospital gown, a video fe…