This looks like it could be Lynn Ann Thompson.
Lynn went missing on 26-Jun-1989, and her car was abandoned in Terre Haute, IN. The UID was found in the Mississippi River on 07-Jul-1989 (i.e., 11 days later). The Wabash River cuts through Terre Haute, and continues into the Ohio River, which then feeds into the Mississippi. This appears to be about a 500 mile distance between Terre Haute and Mellwood, Arkansas.
Is 45 miles per day a reasonable rate of flow for the Wabash, Ohio, and Mississippi rivers?
She is not on the NamUs rule-out list for this UID.
It's a little difficult to match these cases on vital stats because there is no height information available for Lynn, and the age range on the UID is pretty wide.
The UID has several scars (paired in twos) on her left wrist, oriented crossways. This would seem to suggest (if the victim was right handed) that she may have attempted suicide earlier in life. There is nothing in Lynn's narrative to suggest that she has ever been suicidal. But then again, there is very little information at all in her narrative.