From what I have read we are meant to just bury the body and walk away.
No preparing the body for burial.
No preparing a pyre for burning. Definitely no burning!
Just bury the body like one would bury trash or something else they want to get rid of. The point is such a ruh disobeyed and rejected Allah. Such a ruh is destined for the fire. Our loyalty, servitude, fear, love, everything is for Allah. Not the dead carcass of a mushrik.