So, looking into Anna Anderson's case, I found that Benancio Martinez Beltran disappear the same day, only about 30 minutes from Where Anna disappeared. There's no evidence that the cases are related, but it's interesting.
Looking further into her disappearance, she was last seen 12/5/83 but wasn't actually reported missing until 1/4/84. So, there is a about a month of time where she could have very well not been missing. There's also several claims of sightings all the way up to 1996. It looks like she was dating a man named Victor. Her senior quote has "Victor and Anna por vida" which translates to Victor and Anna for life. However, I can't find out who this Victor was. There was only one victor in her school at the time. I also checked other high school year books in the area, and didn't seem to find anything. Doesn't seem to have any connections with her. Her tattoo "H.D.V.O" on her ankle has no significance that I could find online.
There are reports that she started using drugs and began prostitution to fund drug habit. However, I haven't seen anything that supports that other than word of mouth. There have been no arrests for her.
I found her sister on facebook, and I noticed she spells her name as Andersson. They are Hungarian, as it was their mother's native language. With the idea of maybe she just got into drugs/prostitution that she could be alive somewhere, I searched through social media with varying versions of her name and her mother's maiden name Hiszem. Nothing came up. However, when seeing her mother's obituary it does say Anna is dead in it. I don't know if it's because they gave up looking for her or if there's evidence we don't know about.