How do deal with a manic depressant mother?

im 15 years old and she can be so wonderful and fun and loving and amazing when she is 'happy' but then the littlest things can set her off and she just goes crazy! and she calls me names and points the finger at me and sometimes hits me and ill say i hate her [to myself] and be so mad at her but after a couple days shell be nice and ill 'love' her again. of course when she goes off on these rampages its habbit for me to argue back ALL the time and my dad tries to tell me to just let it go but i cant, its not in my makeup to just sit back and let her yell at me and not be able to explain myself. so how do i deal with her? i wnat her to be happy and nice all the time. its gotten to the point where almost everyday we fight. i dont like it. what do i do?