You are absolutely right, they have been very tight lipped and don't have to tell the GP a thing.
I am certain for several reasons.
1. If she had gone through the wood chipper it would have been a horrific scene. Someone would have talked and leaked it, it's just what happens when someone dies in a manner that awful. There have been leaks already popping up all over, they are coming from people on the scene. To date none have been earth shattering, but I can assure you that this one would have leaked long ago, it's just not something you can keep quiet and LE would have known that and not even tried.
2. The media and the shots of the chipper and mulch pile would have picked up on it.
3. If the chipper had been used to dispose of the body the focus on that pile would have been centralized in its path not all over and again someone would have picked up on that.
4. If she had gone through the chipper they wouldn't still be searching for her. The media has said that they have not found her body yet, they skirt the truth but in my experience they don't outright lie.
5. If the chipper had been used there would have been arrests much earlier.
No disrespect taken. I could always be wrong, but I would be floored if I was.