For the address where they “found” her to be linked to her sister’s ancestry.com account, someone had to have linked it. Either she or her sister or some other relative that knew where she was.
That means her whereabouts was already known before the detective “found” her.
So the whole story is anti-climactic …. she wasn’t missing - and she obviously wasn’t trying to hide her location from anybody.
The family knew where she was, but no one bothered to inform the police.
The story doesn’t even mention who filed a missing person’s case back in the 60’s. Her siblings? Her parents?