True, it is not the fault of the person working at the drive through window if your food isn't ready promptly.
Cardinal rule when dealing with people in the service industry: Don't yell at people for something that isn't actually their fault. It might make you feel better but it's really not fair and it doesn't accomplish anything.
With problems like that with fast food, all you can really do is stop going to the restaurant. It's not like a sit-down restaurant where you can send the food back if it's not right, or complain to the manager. I think that risk is just part of the cost of the general convenience of having fast food. But you can, at least, make sure to always, always check that your food order is right before driving off.
With cases like
this, however....
The window lady's answer : I thought you might want to help me feed my kids.
...you can bet I'd be parking the car, marching in, and informing the manager that the lady working the window is trying to steal from people!
Also, I don't know if this has been the experience of other people here, but I've found that I tend to get much better service from local chains. Here in the Dallas area we have Jack's, Jake's, and Burger Street which all have very good burgers (and tater tots! Mmmmm....) and friendly people as well. Those are pretty much the only places I'll go for a fast food burger nowadays, though if I ever get the chance to go to In-and-Out in California, Nevada, or Arizona I definitely will-- hear they're excellent!