How did she stop to make the call?
I don't see the booster being an issue. Maybe the cotter pin broke from the pedal to the booster.
You can see of the MC is a problem, it is right on top.
pads, no way. You would have hit the wear markers that give a nice squeal if they where low. Even if they where to the lowest point they should still stop the car. Lets not forget the rears are most likely 1/4 or more than the fronts on most occasions!
Should have stopped the car fine. Maybe not great but good enough. There are a lot of safety features with braking systems.
Maybe something you did previously as this does not sound like a common problem that spider owners encounter?! Interesting though.
J