I really don't think Misti killed her and hid the body.
I just don't think the things she says make sense.
She may be covering for someone.
Maybe her brother is the perp.
Close by, has a vehicle, hasn't been very visible.
Could have left the house with her, went down to the pond, decided it wasn't deep enough, looked inside that shed, decided she would be found, and then completed the rest of that loop that ends at the train tracks.
She may be trying to throw attention away from her brother.
She may think Ron will actually kill him.
That makes more sense to me than a RSO from another state that we has not been identified, named as a POI, no notification to ask people to look for him. Keep in mind this is suppose to be an armed RSO that is just roaming about.