I haven't had time to get on WS for a few days, but one explanation for the abandoned shoe along Sherry's running route that I don't think has been mentioned yet:
Sherry sprained her ankle/sustained some injury to her foot. Maybe she took off her shoe and was tending to the injury when someone pulled over and offered to help. When I first read about Sherry's disappearance the other day, I had hoped that someone offered her a ride to the hospital and that, with all the publicity, she would be quickly located. Obviously, that's not the case. So, there's still the possibility that, assuming she suffered an injury while jogging, the person who pulled over was NOT a Good Samaritan but someone with a criminal motive.
As for the possibility of the shoe being planted, I'm sure LE has searched in the vicinity of where the shoe was found for shoe prints (signs that she was running and suddenly stopped). If there was a struggle, there would likely be signs in the grass/dirt in the vicinity of the shoe.