Marquez was last seen in Los Angeles, California during April 1998, three days prior to her forty-third birthday. She has never been heard from again. Marquez was the president of ClearGreen Inc. prior to her disappearance; ClearGreen followed the teachings of the author/guru Carlos Castaneda and led seminars based off his methods. She disappeared the same month Castaneda died, along with four other of his disciples. All of their telephone numbers were reportedly disconnected on the same day. Talia Bey, one of Marquez's aliases, was listed on Castaneda's death certificate as his niece.

Marquez's family lives in Puerto Rico and are still searching for her.