I have finally caught up and am horrified by the possibilities swimming through my head of sweet Zahra's fate.
Some of my random thoughts...
I believe that it is possible that Zahra's father may been a loving and devoted father to Zahra, up until he became involved with SM.
I believe that it is possible that Zahra's father also suffered from domestic abuse that caused him to change over the course of his relationship with SM and become submissive to her and detached from Zahra.
I believe that Zahra was likely pulled out of school for SM to have more control over Zahra, as Zhara may possibly have been becoming bolder as she got older and was becoming more of a threat to SM. SM may have feared Zahra leaking too much information regarding the abuse.
I believe that it is possible that the passports may have been in the truck, in the event that they needed to make a quick getaway to alude police for the outstanding warrants and or Zahra's biological mother.
I believe that Zahra was likely killed more recently in a fit of rage by the SM, but I believe that Zahra's father assisted in her disposal.
WARNING - GRAPHIC
I believe that it is possible that they initially began disposing of Zahra via the wood chipper at the house, but that it may possibly have become jammed or broke and the job could not be completed at the house. They may have been feeding additional wood through the chipper to combine it with the human remains to make for more of a mulch consistency. I recall reading that there were logs and a wood pile at the home. It may not have been out of the ordinary for the father to grind up wood at the home on a fairly regular basis, so neighbors may not have questioned the sound of the wood chipper, if he used it regularly.
I believe that they likely transported the rest of Zahra's remains in the Tahoe to the father's work site to complete disposal via the industrial wood chipper, possibly combining additional wood to make the human remains less noticable in the mulch pile.
I believe that once they completed disposal of the remains, they went back home and decided to attempt to burn the evidence that was left at the house.
Finally, I believe that once LE has enough evidence that Zahra's remains are within that industrial mulch pile, they may also need to go back through business records to determine if & where mulch/human remains may have been delivered to other locations in the course of regular business transactions.
Rest in Peace, Sweet Zahra! You are in a much much better place.