The timing of this encounter (which, by the way, appeared to be quite entertaining to the other passengers judging by their smirks and sniggers) was such that, shortly before arriving at our station, the young lady (having made no progress with my mother) turned to me; I had kept entirely out of the discussion until then.
I forget precisely what she said but she was clearly keen to try and recruit my services as another antagonist. The retort usually only occurs to me hours later. But this time it came to me in a flash; so, in my poshest pompously pretentious pronounciation I said “Do you mind? I’m not responsible for my family’s actions. I’ve never been so insulted in all my life!”
And got off the train.