I want to use the attached photo in fairly high resolution, but myself and other background details are reflected rather obviously in one lens of the model's sunglasses. I've tried copying the clouds from the other lens, various cloning/healing angles, and nothing is convincing. This problem is beyond my current GIMP expertise, and I'm looking for help. Please assist, thanks.

Something like this?

Going to be a layermask but then, more artistic than procedural and I am no artist

Not bad, I think you might be onto something there...

Light or image reflection in glasses is a very common problem in my photos. Thanks for sharing a simple way to handle the reflection!!!

Something like that (it's a quicky)?
I selected her right eye with the ellipse tool, copy to new layer, put above her left eye, unified transform tool > rotate 180deg(to have that magenta on the external side) and transform slightly bigger at the same time, a mask using the selection then fine tune the mask (value propagate, then blur slightly), color /hue saturation to diminish the magenta, then curves to darken as this right "eye/lens" is now on the dark side (no pun intended ), then Filters/Map/Displace -1 or -2, just to not look the same at the pixels level, done...
I could have ad a long shadow, with a tiny length and low opacity to match the edges shadow, though...