Robertson lived in San Luis Obispo, California at the time of her disappearance. Over Memorial Day Weekend in 1979, she went to vacation in the Mount Rainier, Washington area. She was last seen in Tacoma on May 27. She and her dog were seen wandering in the Sunshine Point area that evening. Robertson was incoherent at the time. She and her dog were gone the next day, leaving Robertson's belongings behind at her campsite. She has never been heard from again and her dog was not located either, although searchers found Robertson's van within a mile of her campsite.

Both Washington and Oregon police are investigating Robertson's disappearance. Few details are available in her case.