Trouble in the coop

I have a small backyard flock. 7 mixed Americanua, Buff Orpington, White Rock, Golden Lace and Aconnas.
The girls are around 17 weeks old. All has been well in the social structure until a few days ago.
When I let the flock out of the coop and into the yard they run daily, I stand an watch then to check for any problems and also admire them as they grow and change.
The Buff Orpington started to become very aggresive towards me standing at the gate.
THis morning I was awaken by a lot of noise in the coop. Two to three others where after the Buff Orpington and were all over her.
I went out to the coop to assist only to have the Buff O pacing at me at the door and coming at me when I was in the coop.
In the yard the Buff is isolated and being chased and attacked by a few of the others..

New to this chicken raising.. Not sure of what the cause of the change in this bird and will the flock take care of the problem on its own.

 

Thanks for the replies.
The Buff is coming at me and pecking and excited.
Have not thought of it in the light of looking for protection.. Will approach her as that and see how she react,
I did notice how upset she became a few days ago when I had made some changes in their coop with perches and liter..
Do there demeanor change as the get ready to lay?
I will keep my eye on the situation.. Just wonder what has happen to change the harmony in the flock..

Thanks