Why? I think it was another trucker/slayer, known for that route. Some of her injuries seem consistent with this m.o. This poor girl suffered a horrible death, and I pray we find the maniac that committed this heinous act.
Amateur opinion and speculation
I don't think he killed anyone besides Viola Lucas, Kate Rich, Becky Powell, and
maybe (big maybe) Laura Burnsley.
The guy was beyond a compulsive liar. He confessed to literally
thousands of murders that he factually could not have done, in exchange for attention, cigarettes, and strawberry milkshakes. He was a murderer, but has never actually been proven to be a serial murderer. Detectives would tell him information about murder cases that only the killer would know so he could "confess" and then they'd close the case. A great example is Debra Jackson fka Orange Socks, who of course was also found in Texas, a year and a day before WCJD, murdered under strikingly similar circumstances. Lucas was provably across the country, working in Florida, when Debra was killed 1500 miles away, but he still confessed to it after being shown crime scene photos and given details of Debra's murder. And Debra's murder was the one that got him put on death row (before the sentence was commuted by Gov Bush, because it was obvious that he could not have killed her). I'm sure we all know this story, but I always feel the need to bring it up when talking about Lucas, because imo it is the prime example of his lying and the consequences it had, for him and for others. He also confessed to a boatload of other UID and former UID murders he couldn't have or was extremely unlikely to have committed (off the top of my head, Carol Ann Cole, Marilee Bruszer, Tammy Jo Alexander).
I agree that there are high chances that it was a trucker who killed WCJD, probably someone in the vein of Robert Rhoades. I feel she may have been killed in a parking lot mostly abandoned due to it being nighttime (possibly a truck stop parking lot, possibly even the Hitchin Post), or an empty country road.