Problem solved! (CC not cleared from possibly contributing, but wasn't the prime cause either...)
Btw, being hot on a different trail, I never got around to trying some of the recent suggestions here, but would have done so had the 'trail' petered out, which it didn't...but thanks all for your efforts to help, much appreciated!
So for you that contributed, plus anyone else lurking this topic, the problem was quickly solved by the second $ "expert" to address it (B. Rath) on the Just Answer web site...and for a mere $18 no less (plus my voluntary tip)! JA mostly works in real time, and only charges if you're happy with an answer from one of their supporting "experts" and "accept" it. If not ultimately accepted, your deposit (your choice of $12-$18+) is refunded. Site also says it's supported by "experts" from a variety of other areas besides computer related (e.g. doctors, lawyers, veterinarians, mechanics, etc.), so you can bet your boots that I, for one, will have it saved to turn to for any future toughies that turn up! And aside from "free" advice on support forums such as this - which is great when it works - there's no way any pro would have worked on DD's puter for less than 100 bucks or more, even if not ultimately finding the fault with it.
Anyway, off the commercial and back to the solution for this bear - one that had so far stumped me as well as anyone else who had looked at it on 5Star, Aanteres, and TechSptGuy forums as well as here - was simply (you're not gonna believe this!) to disable a default-enabled "ad blocker" (different than a "pop-up stopper" I learned) in the Verizon Security Suite (a Yahoo product I was told later) that DD had been running without a problem for over six months! Although amazed that could do it, and you can believe there's a couple of happy campers that it did, I probably never will understand why the problem only affected Yahoo pages, or why it started only after a CC run...but, I've long ago learned never to argue with success!
nevet