Mother Daughter Problems

Is it me or her? My mother has nagged me and yelled at me for years. It mostly started when my brother started running into trouble. She really couldn`t help him and he ended up dropping out of high school and started getting high and drinking all the time. He moved out and now it is me (16) my little brother (12) and my mom. I am a good kid. Get good grades, stay out of any kind of trouble, respectful, and caring. I think that she may have snapped! She yells at me when she wants me to do something as if she told me over and over again for days but never did. I tell her "why are you yelling at me?" and she says (yelling again) "I am not yelling at you just do the dam dishes" or what ever she wants me to do. One time I helped her spread a chemical around the house to keep bugs away, (acually it was just me). I wore gloves but I started to get a burning feeling above where the gloves covered and went inside to rinse my hands with water. She came inside yelling and screaming at me to go back and finish. I told her why I was rinsing my hands and she called me a liar and to finish. I got angry and said "Fine, if your going to be like that I wont do anything!" and went to my room and shut the door, sitting in front of it holding it shut. A few minutes later she came stomping up the stairs and screaming at me to come down right now. I didn`t answer. She started trying to open the door putting her wait into it screaming nasty names and words like "come out here right now you lazy fucking bitch!" I have never swore in my life especially to my mother. What is wrong with this picture? Did I diserve this? I have lost respect for her after this, which was an unconcious decision. Does she have any right even though she is my mother? Is it me or her who is responsible for these actions?