Originally Posted by CountryRoads:
My problem is that we're outside at the end of the day, at least for a little longer until the weather changes. So, I typically still have other kids here while her children are running the show. It does go better when we're inside, because I'm able to have them standing on the rug waiting to go home.
Dcm won't just grab her kids and go. She sits there and begs them to leave while they play her like a fiddle. Its the strangest thing. I just wanna scream "PICK THEM UP AND LEAVE!" 
Do you have your phone on you? Can she still text, and you send the kids and their stuff to a bench near the gate? If she knows this is a system for kids who (ahem) test the changing of the guard, maybe she will step up? This means you will need to explain that her pick up methods are requiring this procedure.