I think
Ann Linda Riffin, missing Oct. 1983 from New Mexico, might be a good match for this UID.
She is a bit older than the UID estimate, but is the right height and hair coloring. What caught my attention most was the note in the Charley Project description about her religious practices:
She has previously lived in Britain, Israel and Peru, worked as a teacher and a journalist, and wrote articles for the Jewish News in East Orange, New Jersey. She enjoyed humanitarian causes and wanted to be an author in 1982.
Her sister described as a "troubled" and introverted person without a sense of direction. She moved frequently, sometimes staying with her parents, and also frequently changed jobs. She converted from Judaism to evangelical Christianity, and at one point taught at an evangelical Christian school. She had been living in Ruidoso, New Mexico for only a few months before disappearance, renting a room; her landlady said she dressed plainly, didn't date and rarely went out.
There is no mention of the necklace, but of all missing persons within a few hours drive of this UID, she seems to be the best candidate for someone who would own that type of necklace.
Riffin is also noted as having scars on her left leg, which would match up with the UID’s surgical repair work.