I would actually imagine that what she is clutching so carefully (and not interfering with the evacuation since she was probably the last one out) was in fact the bar takings!
I have always respected BOAC's postings and I do not doubt that BA warned him at some obscure point in his career that the 737 could just possibly pick up some possible contamination into the air conditioning system and cause fumes.
I personally would like to see this safety notice for it was never dangled under my nose.
I spent the better part of 40 years landing on contaminated runways in aeroplanes varying from the AW Argosy through the DC-10 to the BAe-146 and I never once heard of picking up fumes from the cat's pee on the runway nor did it EVER happen to me.
Certainly it was essential to switch off your air systems whilst being de-iced; every idiot knows this; but I would love to see an instruction that tells me to de-pressurise the aircraft on finals in case we pick up fumes from the runway
during the landing run.