Picking on Each Other?

Lately I've noticed my five chickens picking on each other.. mostly on my Rhode Island Red, who, I'm guessing to escape it all, stays in the coop all day (which could be an entirely different matter). Could the summer heat have anything to do with it? Usually my red chicken is the boss, but when ever she comes out of the coop, she is always on gaurd, puffed up, and quietly sqwauking, and the other chickens are ready to peck. So far no injuries, usually happens when she tries to eat, drink, roost, or pretty much whenever she goes by the other chickens. She's lost a bit of weight, but she looks ok. I'm starting to take her out of the coop every day for a good hour and hand feed her vegetables, water, and grain to make sure she gets some food down her. There are three different breeds in my coop, I have two black sex-links, two buff orpingtons, and the one rhode island red. I'm not sure if that could be the cause of anything, especially since they have been together since they were chicks. They are all relatively a year and a half old. As far as their living arrangements go, they have a six nest, two story coop (but they all seem to want the same nest at the same time), with an attached run that they go in whenever they want, usually all day. I let them outside of the run/coop for a good hour or so everyday. Do you think if I let them out longer it will ease some of the tension? Any ideas, suggestions, or anything would help as to why they are suddenly so ticked at each other and how I can stop it, because I really don't want any injuries