Even after reading about Amy's neighbor, I am still thoroughly convinced Amy is Blairstown's Princess Doe.
My theory is that Amy went with her neighbor Raymond Diaz and his wife (either willingly or unwillingly), who possibly raped her and then sold her into the sex trade. She was sent to New York City where she remained until she was murdered by Arthur Kinlaw (for whom it sounds like she was working as a prostitute.)
It certainly sounds like Diaz had sex trafficking connections, especially given his threats made towards Amy that her friend recalls. Isotope testing on Princess Doe shows she grew up in Arizona but had spent the last 5 months (at least) of her life in Long Island, and between 7-10 months before her death she spent time in the midwest/northeast. Amy disappeared November 1981--Princess Doe was killed July 1982--8 1/2 months later. What if she was sold to a person who brought her across the country and through the midwest and settled in Long Island, where she was sold to the Kinlaws who then murdered her for some reason? What if Diaz and his wife claimed they killed her knowing that her body would never be found (since she wasn't dead), therefore they'd never be convicted of it? It sounds like Diaz was messed up on drugs, hearing how he showed up at Amy's house naked antagonizing them. People will do crazy things if they're addicted to drugs, such as befriend a teenager and sell her for drug money. Also, I'm guessing that most girls who are kidnapped and sold into the sex trade are forced to use drugs and develop a drug habit, making it nearly impossible for them to leave, which would explain why Amy (according to my theory, anyway) worked as a prostitute for nearly a year before being killed.
I am wondering who told Amy's sister she was raped, murdered, and buried under a bush in the desert?