I figured she was in the Barn... My Partner hates me, I always tell the end of a story... Logical deduction actually, writers are so predictable
I'm finding the series to be annoying. These survivors are going about the whole 'surviving' thing wrong.
Take that RV and its breaking hose... If you can't fix the damn thing its time to dump it for a vehicle that runs. It was just stupid for them to drive down the highway and keep on going when they reached the pile up. Where is their front scouts?
If it was me organizing this, I would select a bus - one that runs , a new one. Gut the damn thing and have steal mesh welded on the windows. Install a top side 'cage' that allows people to access it from the interior, with gun slots, have somebody top side while going down the road to see farther ahead.
Hit a warehouse or cannery for food, not a store. Run two bikes 5 miles ahead to scope out the terrain ahead. there would have been no lost Sophie as the children and infirm would have been locked inside the bus. Find a warehouse, one with sun-lights (roof windows) seal it up, and wait out the decay - eventually those corpses will rot to the point where they can't poise a problem.
Lots of stuff can be done, this group seems to have a death wish.