How are Mary Jo Kopechne and Senator Ted Kennedy related

On July 18, 1969, Kopechne attended a party on Chappaquiddick Island, off the coast of Martha's Vineyard, Massachusetts, held in honor of the Boiler Room Girls. It was the fourth such reunion of the Robert Kennedy campaign workers.
Kopechne left the party at 11:15 p.m. with Robert's brother Ted Kennedy, after he — according to his own account — offered to drive her to catch the last ferry back to Edgartown, where she was staying. Kennedy stated he made a wrong turn on the way and came upon a narrow, unlit bridge without guardrails. Kennedy drove the 1967 Oldsmobile Delmont 88 off the bridge and it overturned in the water. Kennedy extricated himself from the submerged car but Kopechne died, after what Kennedy said were several diving attempts to free her.

Kennedy contacted several aides that night, but failed to report the incident to the authorities until the car and Kopechne's body were discovered the next morning. Kopechne's parents said that they learned of their daughter's death from Ted Kennedy himself before he reported his involvement to the authorities, but that they learned Kennedy had been the driver only from wire press releases some time later.