I may be in the minority here, but I think it’s very possible that her body is in Idaho.
PF went to all that trouble to make it appear that Kelsey was in Gooding, alive and well, at the time those texts were sent. IF he thought beyond that, beyond just doing that to buy him time and distance...it makes sense that he might also think “Ok, I’ve made it look like Kelsey was here in Gooding on the 25th. How can I make that falsity even more believable? I know, I will bring or have somebody else dump Kelsey’s body nearby. As if somebody else, probably random, came across her here and killed her.”
At least that makes sense to me. Why kill her and just leave her in an area close to him if he’s trying to prove she was en route to Washington? Why not dump her in an area that coincides more with the phone ping location?
JMO, and I realize he might well have disposed of her body right after the fact, much closer to home. Just throwing out another possibility.