A 6-year-old girl died yesterday of injuries she suffered in an accident on the Massachusetts Turnpike, State Police said. Jennifer J. Ortiz, 24, of Framingham was driving a 2002 Acura RSX eastbound on the turnpike when her car went down an embankment, rolling over three times, State Police said. Ortiz was accompanied by a 5-year-old girl and the 6-year-old victim, whom State Police did not identify. All three were ejected from the car and were transported to Massachusetts General Hospital, where the 6-year-old girl was pronounced dead. Ortiz was cited by State Police for a marked lanes violation and for not wearing a seat belt. State Police said evidence suggested that no passenger was wearing a seatbelt.