I don't normally suggest that the person is still alive, especially after all this time... but, looking at it objectively, we have a young woman who was raised in a single-wide trailer with ten other siblings, was abandoned as a child by her parents through institutionalization... she admitted to physical and verbal abuse from her family, had a history of substance use disorder and addiction with her mother, and her mother didn't seem to make an effort to find her... Objectively speaking, it doesn't seem like an environment anyone would want to return to...
Some obvious variables make me question her life, of course... the abusive boyfriend, the failure to contact DFS to ensure her siblings were well taken care of... However, these same variables could also be considered factors that led to her disappearance... not only did she not have family support, but her boyfriend was abusive, and he also had a criminal record? This girl can't catch a break... totally overwhelmed

In most cases, it seems highly unlikely that the person will be recovered alive... given that this woman disappeared in 1973, a time when self-identification was much easier than today, I sincerely believe this could be a case of runaway and relocation... I don't think she wanted to be found... and with good reason...
and... The abandoned checks make me think... but it's possible that she felt the need to run away (from her boyfriend?) too urgently to get back home to get them, and she still did it...
whatever it is
Rest in peace, Sheryl