* Myrtle's Death: Myrtle was murdered by the Basilisk in the Chamber of Secrets during her time as a student at Hogwarts, around 50 years before the events of Harry Potter and the Chamber of Secrets.
* Tom Riddle: The Chamber of Secrets was opened by Tom Riddle, who was a student at Hogwarts at the time. He was later revealed to be Lord Voldemort.
* Basilisk's Control: The Basilisk was under Riddle's control, and he used it to terrorize the school.
So, while Myrtle was a victim of the Chamber's opening, she was not the one who opened it.