Perhaps the ME had never seen a body doused with bleach, and wasn't looking for it in his analytical tests. And, alas, Danielle's body has been cremated.
We do know there was an usually dehydrated or mummified body, skin very dark in color, few recognizable internal organs, teeth missing, unusual delay of bug activity.
A bleach-doused body does not necessarily implicate DW. It could have been whoever disposed of the body - any of the usual suspects.
Dousing with bleach seems like something a person would do to remove DNA evidence from a body. One could also douse in gasoline and ignite, but that attracts attention.
I have a hard time thinking Danielle was kept somewhere besides Dehesa for several weeks before being dumped there - whoever the murderer is.