I'm not certain who this 'elderly lady,' is- but suffice to say, that even if you somehow Did manage to secure her, who's to say that that would've done the trick? And that then it just wouldn't have been some-thing else?
It's like that whack-a-mole, game, maybe? Poor analogy, I know... but it's no use in beating yourself up for things that are not in your power to control (their actions) & also, how futile it can be to question yourself, if in fact, as I said: "If it wasn't this, it would've been that!" So while it's natural, and understandable, because you want so much for it to be (so) - but you can't necessarily will your way into someone else's head/body/mind/spirit/soul... ya di ya di ya da~ & change their thinking, or tell them to do something they are dead set on, or against (in/doing).
Hopefully, that made some sense. Because, now I'm beginning to fool & confuse myself! Try not to let it spend to much time in your head today (the thoughts, & the regret, or whatever else). As it is not healthy, nor productive. And won't help you in whatever future endeavors you look to tackle with this individual (if you are just wearing yourself out).