My coworker will promote to my leader, how i to get along well with her?

During work or office time, I think you should give the respect due her as your immediate superior. Do not take advantage of your status as her best friend. It is you who should give the first recognition and acceptance for her position so that others will do the same. I think positions in the office or work should not affect your friendship. After office hours, you can go back to your old selves...to the same best friends relationship you have.

It is good that she gor promoted. I am sure you are happy and proud of her. You should not worry too much.. i guess since she is your best friend, there should be no problems to arise if you still do your work as you are doing it now. Support her in every possible way as your immediate superior, of course do not expect she will favor you all the time for being your friend and do not be too sensitive if she corrects you on some things... :) im sure you will do good. Good luck to both of your.