If you want to make this employee your first stop, you need to stop thinking that she is the problem. The real problem is your boss. He is enabling the very behavior that you are trying to extinguish.
You should let your boss know that it is fine if he meets with any of your employees at any time, but there should be some agreed-upon ground rules. For example, your boss’s first step should be to see if your employee has already communicated her thoughts and concerns to you. In some cases, she may have justifiable reasons for not doing so, but in most situations she should be directed back to you for the first pass. Let your boss see the advantages of this strategy, such as in terms of saving his time and demonstrating support for the individuals who report to him.
At the same time, you should look at the way that you deal with this employee’s input. If you constantly reject or ignore her concerns, her desire to go around you is not surprising. If you truly believe that you respond to her comments professionally and quickly, she should be advised of the same ground rule that applies to your boss. Namely, although she always has the option to take advantage of your boss’s open door policy, she should try your open door policy first. | 
