Frequently in calm water I will completely open my upper hand - paddle rests in the hollow between thumb & index finger. On the pull stroke, I often just have my finger hooked over the shaft - no thumb grip.

Of course, when the water gets rough, my grip tightens considerably!

If you could rig a strap that holds the paddle during the pull stroke, then she cradles the shaft in her hand on the upper "push", it might work. The other hand would have to be doing all the work of alignment - whether paddling feathered or unfeathered.

Any strap rig would probably interfere with changing grip position. You might be better off focusing on the "whitewater philosophy" of keeping the same grip on the paddle at all times.

Another whim - instead of a smaller shaft, think about a native paddle (gripping around the blade) or a large padded section on a Euro paddle - like closed-cell foam wrapped around the shaft. Maybe this would be large enough for her to grip?

Just guessing here. Hope some of the suggestions from this forum will help. It's tough to know for sure what will work without knowing the lady & experimenting.

Val