I don't think they were hiding or necessarily waiting for her - I doubt anyone knew she was going back there alone. I'm thinking someone that had it in for Shonda just happened to be there when she showed up again. I also think whatever happened to Shonda happened after she left there. Like someone followed her and either ran her off the road or blocked her way to force her out of her car.
Once again, totally agree with this. This is also what everyone in town thinks, she was followed as she was leaving town (hence the cell ping north of MW) and she got into it with some girls and things went wrong and then the guys were called to cover it up. I'm glad her story will be covered again tomorrow evening!