Anti, thank you for doing my thinking for me this morning. No, I had NOT changed out the USB cable, because my feeble mind thought "Hey: the phone's charging... cable must be good!"
I did, however, just swap the cable out and plugged in Ginny. DING! "Open folder to view files" pops up every time.
So: it's a PARTIAL cable failure, something that I can admit I have not seen in a long, long, time. And now we have the laptop back to its eccentric self. Thanks again!