I just tried some 165 mm cranks, and they were a revelation for me. Very good for hip pain compared to the 170's and 175's I've been using for 30+ years.
I'm thinking the reason they work for that is, my hip is not flexed as much at the top of my pedal stroke when I'm applying power, as it would be with 175's. And when you do something like climbing a ladder, you will find that when the hip is flexed a lot, you have power, but not as much as you do as the leg straightens out, since we have an increasing ability to apply power as the leg straightens out.
So a shorter crank requires less hip flex with each pedal stroke, puts the leg in a more advantageous position at the top of the pedal stroke, and reduces the range of movement required for each revolution. I can really see this adding up over a 50 mile ride that requires thousands of pedal strokes, some under very heavy load.
To my mind, this is a different way of attacking the problem of reducing hip flex, via the crankarms, rather than attempting the same thing by having the rider sit up more, which will cause a whole slew of problems in and of itself by putting more weight onto the seat. Might be worth a try for the OP, especially if the woman has shorter than average legs, she might just need shorter crankarms.