I made the trip from the Hitchin Post to Ellis last week. I took the 1696 exit (Pinedale Rd, north of the Hitchin Post) and went a long way their, but then returned on the 19 (south). So, someone could have given her directions leading to the south or north of the Hitchin Post. That said, I don't think she ever actually left the Hitchin Post alive.
This trip to the Ellis Unit was a very creepy drive. It's literally in the middle of nowhere. I guess I would have to assume she didn't know that. One thing did occur to me while I was out there - could she have actually been planning to go somewhere that she knew or heard about and the Ellis Unit was the landmark to find the place? There isn't much out there, but in the 80's there would have been a few farms/ranches, and a couple of churches in Riverside, the town adjacent to Ellis. So a hypothetical would be that someone said to get to my house, or the the church or whatever, "you go towards the Ellis Unit but turn on XX road about a half a mile before the prison."
I'm not sure her response that she was going to see a friend at Ellis really means she was going to see someone at Ellis. I have a 13 year old and half of what he says really means something else. So, hypothetical again, maybe the waitress said "Why are you headed out there" and she just said "to see a friend" Could be true, could be BS, could be she was going to see a friend somewhere in the generally vicinity.
It was a long drive to the Unit - I had a lot of time to think