Thanks to all for your explanations. I wish I could have provided better info initially, but English is not my wife's first language, and even then, when it comes to anything remotely technical....
At least in my wife's case, she took it all in stride. Can't speak for others on that flight.
We're both pretty experienced travelers and don't generally get upset by these kinds of delays. Overall, she was quite pleased with BA's handing of things.