If the female caregiver is responsible, then I think she was perfectly capable of manipulating the other two people that day. I get the impression that, after a significant amount of time (not 5 but maybe 25 minutes or more), the foster grandma realized that neither Wm nor the female caregiver had returned so she went in search of -- not into the house but around the corner, the direction both Wm and the FC had gone. When she didn't find them, I think she alerted the neighbor and was genuinely confused for how two people could vanish. I don't know exactly when or how the FC arrived back home without being noticed but I think she likely convinced the foster grandma that mere minutes had elapsed and that she'd been searching outside/nearby and that they should together go inside to search, where she then doubled down, calling LE saying Wm had only been gone briefly and the only delay was minor, the time it took her to "search the block" and then the house, IMO completely erasing her drive time from both her timeline and the foster grandma's awareness -- as in, remember how we are on the patio, then Wm went around the corner with a growl and then I went to look for him and just a few minutes later you and I went inside to search for him?
How much easier to manipulate the story with a young child, the FD. As in, you were drawing, Wm roared, we starting looking for him within minutes.
I would like to have asked her, Big Sister, you were coloring. How many pictures did you draw from when Wm left the patio until everyone was worried he was lost?
She might not have been any better at quantifying the passage of time than the foster grandma, but I can imagine she might've had a fair sense of how many drawings she knocked out during that gap!
My point, should it be lost in my paragraphs, I think the female caregiver was successful -‐ at least for a very long time -- convincing young foster daughter and old foster grandma -- that ten minutes elapsed when closer to 30 or more did!
And I don't think she would have told anybody about the lil drive she took, except that the truck driver engaged her in such a way she had to cop to it.
How familiar was she to the area? Didn't know cross streets. Did she know landmarks? Did she pick a random one of which she was marginally aware, to pretend that's what she was driving to? Only she didn't? Did she pull off the side of the road, go deep into the bush (scratches, cuts?), and was just getting into her car when the truck driver came 'round the bend? And she volunteered (presplained), oh me, I was just stopped her to lean out the window and call for him. Nope, nothing to see here. I wasn't outside my car at all. Just me, in the car, calling out.
Suss.
FWIW I still maintain that there's a fair chance that wherever Wm may have been placed on that dreadful day, it's not where he stayed.
JMO