LE has maintained from the begining that Misty's was the key that her stories were inconsistant so therefore that tells me that Misty did not pass her first Poly with LE.
As far as the details go, LE nor Ron or anyone else in the family are required to tell us anything pertaining to the investigation, so we do not know if Ron had told LE the bed was made, LE may have gotten Ron involved to keep an eye on Misty til they can find something to charge her with.
Lets face it Misty is not very smart, and if she is love struck by Ron they may have felt that the best way to keep her around is by having her believe Ron is on her side. Could it possably be that Misty's brother was the one molesting Misty, and maybe Misty found out that he had messed with Haliegh and she thought that Ron would leave her if if Haliegh told her daddy that Misty's brother had messed with her, and Ron found out that he had messed with Misty to and Misty never said anything. Maybe Ron and LE now suspect that and that what has caused the firestorm between Ron and the Croslin's.
I am just throwing theories out there. I 100 percent believe Misty knows what happened to Halieghand I believe NOW I didn't before but I believe that Ron may be tring to get Misty to break.
The fact that Misty is only 17 and is still a minor may be one reason LE is dragging thier feet, once she is an adult I think they would have more options.
All things posted above are just my opinion.