You might address the state of alert of hers when you talk to each other. Just make her aware that you are seeing that stae and do worry. Do not try to point out that it is damaging or hurting. Just make her aware that people around her take care. But this might only work or be appropriate when you have some sort of personal connection that is a bit better than just between boss and employee. When things are just like that you need to be very diplomatic and careful and try to be just a careful human being. And pull out quickly in case when you face anger or rejection.