My neighbours dishwasher filled up so that when she opened the door there was a few inches of water ready to flood her kitchen floor.

I reckon it is a sensor fault. I dug about on the internet, and it suggests it is a flow meter that tells the machine how much water is in there.
( https://www.how-to-repair.com/help/b...replace-parts/ could even be the same machine)

How does the flow meter tell how much water is in there?

or I am barking up the wrong tree?