How to deal with little sister?

Unfortunately, I have a little sister who tormented me. My mom obviously doesn't seem to understand or care. My mom is too tired from work, cleaning and cooking all the time. I've grown weary of the fighting and my sister just keeps on tormenting me. She makes fun of me at school, and embarred me in front of all my friends. I do not believe in hitting girls, because hitting girls is wrong. She is 12, and I am 13.5 yrs old. I don't want to deal with her, and she has done so much damage. Yea, yea, just kids, fighting. To me, it has affected me deeply. She lowered my self esteem, she put me through a phase of depression, and she obviously doesn't seem to care. I don't want to get into great detail and make this any longer. I just need advice. How to deal with her. It just 'sucks'. I'm going to high school next year, and I cant have this eating at my core. I'll pretend not to care, but she'll just keep on messing with me. And then comes the fighting. ugh.