If it really has gotten to the point where assault is a likely occurrence, then help the lady find a new job ASAP.

If it is primarily a matter of dealing with fear, then encourage the lady to develop mental and physical toughness by participating in martial arts, rape defense classes, "verbal judo" instruction, and developing a few of the strategies offered in this thread.

Suggest the lady make as many friends with co-workers as possible; if the problem is common they may welcome mutual aid and support agreements.

Perhaps the lady knows a cute cop or two she can invite to see her place of work for a friendly drink during her off hours, etc.

If the lady chooses none of the above and to remain a physically attractive shrinking violet who telegraphs helplessness, then perhaps psychological counseling can help, hopefully before anything too horrible occurrs.

Finally, it is her life and her choices not yours. Be a friend, but defend your own psychological boundaries by not feeling ultimately responsible for what happens in her life. Once you have done your best, back off.