Yeah, after looking at some online anatomy stuff (gotta avoid the actual cut up hand pics, tho! zoinks!) I'm convinced you both are right -- the only odd thing was that the condition failed the normal tests she ran on the hand tendons. It's definitely not trigger finger, but I suspect it's similar.
As its worsened I feel it more in the index finger itself, and up the arm, where she certainly located all kinds of stressed tendons.
It also occurred to me that in the past couple months I've worked on playing/singing without a capo on quite a few songs, and on new songs I've been playing repeatedly. As you all know playing chords in the first/open position vs capoed at the second or fourth fret pretty radically shifts left arm and hand position, not to mention the added strain from fretting. That probably has amped up the technique issues.
We're headed to Hawaii for two weeks on Christmas day (and not taking a guitar as I normally do); if that doesn't cure it, nothing will
and I'll look into specialists; even if it's not like it's cancer, though -- it's not like it's going to spread, so while entering the time consuming maze of specialists may indeed offer a faster solution (but only maybe, and in my experience never yet), there's no actual larger threat to trying the simpler solutions first.