回复：老板找人backup我， 看看我老板的email。如何让老板明确我们的分工

你的警觉是对的，这种搞法有些异常，如是我的话，总体来说我会以不变应万变。我认为你可以采取以下措施：

Towards Boss - implement what he wants with no question asked. you should show your attitude that you will do whatever boss wants you to do and gain/maintain his trust. For example, you should send an email to the team immediately and cc boss the newcomer that you welcome her and her experience will bring positive results to your group, etc.

Towards newcomer - 主动出击，give her some responsibilities and even some people （some lazy,incompetent, hardest to deal with people) in your group. Give her project to do. (treat her like people reporting to you). leave the best project for yourself, but don't give her hard one as well. Reporting all this to your boss. So she will start to share some reponsibility of the performance of your group. What I want to do here is: don't let her go to your boss and ask for some particular project and some particular assists she wants to have. I am sure your boss will give her whatever she wants. Then you can't do anything about it.

To yourself - perform best you can do on work. try to understand why your boss likes her so much (maybe talk with folks at her previous department, etc). And you can do something along that line.

To yourself again - worst case, if she is so good and capable, 是金子总会发光的，you might need to accept the truth that she can do a better job than you. In that case, if you don't want to leave the company, you might end up with reporting to her. So if you don't give her a hard time right now, and provide help she needs, then you can at least maintain a good relationship with her and be able to work in the company until retire. This is actually nothing new, I saw lots of this kind of case, and the guy got replaced is happy to work in the same place because someone can do a better job and make the organization strong and last.

Keep a good attitude and deal with it professionally. Good luck!