Of course there are things beyond your control that can cause you to miss your flight, though most often they also cause your baggage to miss the connecting flight as well.
While you can't control all the factors that might make you miss a flight, you can still control your own actions in the event that it happens.
I've missed a good number of connecting flights. I used to travel regularly for work.
I've never pitched a fit at the airline employees. It's foolish and counter-productive.
Ive even seen airlines board everyone, then after learning the delay is going to be over an hour, they let everyone deplane and reboard again. There are always exceptions and if you fly often enough, you see them.
There are lots of exceptions when your outbound flight is delayed. It's awfully rare where they will hold up a plane and make everyone wait so they risk missing their connecting flights because a straggler is running late (regardless of if it is their fault or not). I've seen them wait to close the airplane door as long as possible when they know a passenger is on the way, but once that door closes, I've personally only seen it open if there were mechanical problems with the plane that delayed the flight.
Not mentioned, but....
Perhaps she was late at the gate due to time spent in the bar?