Here are a few more details regarding "Cathy" that I should probably add to the mix.
According to the brother (the sister doesn't remember this detail), "Cathy" told him that she had a friend who was incarcerated in the Sugarland Prison, and at one point, asked his step-father if he would give her a ride to Sugarland. Apparently, the stepfather didn't give her the ride. The stepfather drove a 1978 Ford Truck with a camper on it. However, the brother says he recalls that the couple drove a large American car, possibly a chevy, possibly maroon or brown in color. He recalls that it had a beige or white vinyl top.
Of course, if this is true, it would make "Cathy" a very strong possible for WCJD, despite that her friend was in the Sugarland prison, not at Ellis, and that the couple's vehicle was maroon or brown (as opposed to blue - as was reported to the WCSD by the owner of the gas station who saw WCJD prior to her death).
When he first told me this story, he was saying that the motel was in Richmond, and he even drew for me a diagram of the layout of the motel. There are no motels in Richmond, and after many hours searching Google maps for of the motels throughout the area, he came back to me and said that he thinks that the motel was actually in Beeville. He pointed me to the Esquire Inn on St. Mary's street in Beeville, and said that he is pretty sure that is the same motel. The sister agreed that this appeared to be the same motel, and its layout is very similar to the drawing that the brother gave me.
I've been reluctant to mention these details (1) because I wasn't sure if the brother was just repeating details that he had read in public narratives related to WCJD, and (2) his sister couldn't corroborate those details. The sister was only 10 years old at the time, so it is understandible that she wouldn't remember every detail about the few days that they knew "Cathy". But I've decided to go ahead and put it out there and let everyone decide for themselves whether it is credible or not.