And how would IRCC have issued a visitor visa? Is it that IRCC couldn't connect her current passport to her old PR status from 60 years back?
Basically yes. Not, not 'couldn't', but 'didn't' - either automatically or they had no reason to check.
For files that are computerized, they are quite good at not issuing visitor visas to PR holders. But for older files - not always. I don't know exactly what dates are 'cutoff' - I know that they stopped issuing the 'record of landing' paper sometime in the last 20-odd years (mid or early 2000s I believe), and I think the computerization / digitization was around then.
I believe I read that they digitized / computerized
some files especially recent ones before that unknown date, but clearly stopped at some point digging back, assuming that mostly the older files weren't going to be relevant and/or could be hauled up when needed. But just cost of going for 100% of all records was never going to make sense - not that many PRs from the 60s going to return like in the case above.