what happens when a bird starts plucking out their feathers?

my mums love bird, Cyan(girl), has started plucking its feathers out and i would like to know why. i heard it's from stress and when they start they don't stop. some things that might have caused this is because she is in my mums room and my mum has recently moved her bed around and cyan is no longer at the window. another thing that could have done it is that i have a budgie in my room. also i just went on camp, now i'm not sure how that could have affected her but it started when i went to camp. if you can help me by giving me info on this i would really appreciate it. thanx.