Aisling Brady McCarthy, 37, surrendered Tuesday at the Burlington, Mass. office of the U.S. Immigration and Customs Enforcement, spokesman Shawn Neudauer confirmed.
She's been arrested and placed in federal custody, pending her deportation to her native Ireland.
McCarthy had been charged in the 2013 death of Rehma Sabir, of Cambridge. On Monday, prosecutors dropped the charge after the medical examiner's office revised its original homicide ruling.
The office determined Rehma had a possibly undiagnosed condition that made her prone to bleeding and may have contributed to her death.
McCarthy's deportation is being expedited at her request and her departure is "imminent," Neudauer said.
McCarthy had purchased a plane ticket to return to Ireland and hoped to voluntarily leave the country Tuesday evening.
But Neudauer stressed that McCarthy is a "significant visa violator" and will be formally deported, meaning she will likely face a minimum ban of 10 years before she can ever return to the U.S.
McCarthy's husband and some of her immediate family reside in the Boston area.
She entered the country in 2002 on a tourist visa that only allowed her to stay 90 days. She doesn't have the right to a federal immigration hearing on her case because Ireland participates in the U.S.'s Visa Waiver Program, Neudauer said.
McCarthy's lawyers, who helped coordinate her surrender, didn't immediately comment.