If you have to walk on eggs when dealing with an employee, it is often a matter of time before something cracks. And, since you are dealing more with personality than job skills, this is a particularly difficult matter to unscramble.
By saying that this employee does a very good job, you are obviously satisfied with her technical skills and ability to get her job done. However, if there can be problems every time she interacts with another person or department, perhaps her overall performance is not that positive. In a word, her volatility is likely to interfere with her work as well as the work of those who must interact with her.
It may be helpful to give her feedback when she displays her difficult behaviors, and let her know about the kinds of problems, career limitations, and consequences that can accompany such behavior. You can also suggest more productive ways for her to act and react.
At the same time, since she does a good job technically, it may also be worthwhile to try to build the job around her strengths, and minimize the amount of interaction she needs to have with others. The idea is to let her do what she does best, and prevent her from doing what she does worst.
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