Companies like Zappos are experimenting with flat management hierarchies, in which no one has a title or a boss and the organization revolves around the work that needs to be done, not the people who tell others how to do it.
You may have worked on the same team together as peers, been classmates in school, and come up for promotion at the same time. But only one of you made the cut this time, and it was not you who was promoted. Now your peer is your manager, and as much as you resent it, there's little you can do but accept her in her new role. Assuming you’re not in a rush to head out the door, here are a few ways you can handle the transition.