Thanks for the comments- well yes, perhaps I should have said stereo typical elderly lady.
I think, in fairness to the check in people she was not actually allocated the window seat because there was some shuffling around in that row -the gentleman travelling with her while also no spring chicken was tall and quite fit looking and I think he would have managed ok .
Regarding your check in comment BA have a habit at LGW of altering the type of 73 used on many trips which means if you check in on line you often get a different seat from the one allocated as -for example a 300 is swapped for a - 400. Thats why I thought and think the cabin crew have the final responsibility for making sure the cabin is secure and the relevant rules in that respect are complied with
Anyway was only a question out of interest and thanks both for taking the time to comment
PB