OK, a few comments from a guy who shot about at least a gazilion headshots from actors and models to realtors and corporate execs while I was still in business.
Headshots have two pretty much unrelated purposes. The first purpose is obviously to show what the subject looks like. But the second is to cause the viewer to think "This is a person I would like to work with". Unfortunately your shot does not do the second. I don't know if it's anger, fear or apprehension in the facial expression, but it would not make a viewer want to hire with her. That's why so many head shots (or any other PR
photo) shows the person smiling. She's a very beautiful lady and you did show that, so try again and go for a more pleasant expression.
Then there is the crop, but you already know amputated arms don;t work. I didn't see the one you described as being too tight so I can;t comment on that, but I would suggest splitting the difference.
As for the pose, instead of leaning back, have her lean forwad a bit with her shoulders at a slight angle to the camera. Often leaning back is seen as 'withdrawal', whether valid or not. Leaning a bit forward is more likely to show energy and interest. Shoulders squared to the camera is almost always static. I would recommend not using that high back chair in a head shot. A chair with a back makes it too easy to lean back or to slouch and the top of the back is sort of distracting. Plain white backgrounds seem to work best.
Lighting? You nailed it! Don't change it, other than possbly adding a slight hair light, but that is't vital at all.
Try it again - she's worth it!