I wondered something like this as well! Like others mentioned, it's really strange that the FD and EMS didn't come to the scene until everything was almost done. The Grandmother was there almost the entire duration of the search. The police seem firm on there being other POIs.
So, I wondered if they did find her or at least determine her whereabouts but aren't confirming it to keep her safe or if they did find her, to keep an important witness safe from whoever is running this. Maybe they just need to buy some time to catch up to whoever orchestrated this. I know this sounds crazy but my brain just keeps trying to make the pieces come together and still produce a happy ending for Cupcake.
ETA: so sorry it's still my first day but it looks like we are supposed to MOO at the end of our posts. I googled it and I know we aren't mooing (haha I make jokes when i'm flustered) but everything I said is just MOO.