I don't have any advice, but I am in this exact same situation right now. I've only received input from one other teacher on my team that she notices it too. I would never ask the others because they are very much in the same clique as the "friendly" teacher. Her relationship with the P is very inappropriate in my opinion. Greets him every morning by going into his office and closing the door behind her. Eck! Even if nothing is going on, the favoritism being displayed is nauseating.
I have begun to tread very carefully around her. I don't trust that every little thing I say will not be repeated back to the principal. I agree with goldenbeads. Document what every person on the team should be doing and whether or not they are meeting their obligations. That way if you do need to address it with the principal, you will have proof, and he can't just side with her because they're in love
I wouldn't go to a different administrator though. You don't want to upset the principal.
Ah - have schools always been soap operas?