Yes, she certainly has the look of someone who knows what a huge amount of work these piles of cards represent. There would have been no turbulent kids running around these.

She lives in the Mary Poppins house and has to stabilize her stack of cards like this every time the neighbour fires the canon.

one can number them with a pen, and then find the missing one or guess what was there

All your need to do is drop in one card randomly with all the holes punched out to screw up those things... there was a name for doing that to be a dick but I forgot and am drunk right now so I don't feel like looking it up.

i copied that image from the article of the post without reading that article itself. But, since you asked, i went in that article ... and all i could find is this :

The image of 62,500 punched cards neatly stacked in rows serves as a reminder of the immense physicality involved in early computing.

So, unfortunately, the nice lady might just be a "banana for scale" here 😯 !

I remember our first personal computer had 40 columns on the screen, but we ended up getting an 80 column graphics card for it.

I taught myself basic, but the first language I took in college was fortran, and it was on cards. A bit of an aberration: they had moved on to somewhat more modern equipment, but the lab was being upgraded, so they reverted you the card system for a semester temporarily. It was out of date, but not wildly so at the time.

Well, it might or not be a line of code - depends a lot on the language. It's 80 bytes, and a byte is one character. You could have continuation cards if your line was more than 80. That wasn't ever needed for assembly language, rarely for Fortran, but very common for COBOL.