I don't have any sort of idea or theory about what happened to Shannan. However, I do have the following to share:
It was reported that she was dressed in skinny jeans. These jeans were supposedly not on her body when it was found. I recall reading earlier in this thread that LE claimed she either took the jeans off as she ran through the area in which she was found, or the jeans fell off as she ran.
I wear skinny jeans on a regular basis. One could run a marathon in them, and they would not simply fall off unless they were 15 sizes too big. I doubt Shannan was wearing jeans that were 15 sizes too big, so IMO, it's impossible for them to simply fall off. I also don't believe that she took them off as she ran. If she was running, then she believed that she was pressed for time. Taking skinny jeans off while running is not an easy thing, and it doesn't make sense for her to do this if she was trying to escape.
If you don't believe me, just grab a pair of skinny jeans and try it. Trust me, it is very difficult.