I continued to obsess over this last night, and I thought I'd share what else I was able to come up with.
My first thought was to track down the kid that found her. If he was 10 in 1990, he was likely in my class (the entire county goes to one school) and I was amazed I'd never heard the story from any of my classmates. Doing a little research, it looks like no one took down the name of the child or his parents, but they were believed to not be long-term residents. I think I read they they worked at one of the 2 huge chicken processing plants in the area, as a lot of people do.
There are a lot of immigrant workers at the plants, and they tend to come and go from the area quite frequently. This made me wonder if our girl was maybe one of them (in which case she might not be missed immediately). It does puzzle me that they list her as Native American as opposed to Hispanic when the bone structure usually very similar. But clearly they would be the experts and not me!
Anyway, from what I read she had a lot of expensive dental work (including past braces, which are usually purely cosmetic and quite pricey), which doesn't really fit with the "struggling immigrant" profile of a lot of he plant workers. I hope that mass generalization doesn't offend anyone... there are certainly exceptions.
Given the implied affluence, I'm still leaning towards "resort guest". I wish there was some way to look at the Ginger Blue records from back then, but it went downhill and changed hands multiple times. One of the chicken plants eventually purchased it to use as low income housing for it's immigrant workers, at which point it became a total slum due to overcrowding. Not long afterward, it burned down.
I talked to my sister who was a housekeeper there when she was in high school in '86 - she said the main resort was primarily open during the summer, but some aspects, especially the restaurant and maybe some of the guest cabins, were open year round.