Please help me im going insane!!!!?

she is driving me crazy... a bunch of girls were teazing her that she was neardy and ugly so i helped her through her self esteam and make up.. i tought her different hair styles and now she is so ungreatful!!! i mean i don't want her to thank me or any thing... i just want her to give me a lil respect!! now she thinks she is preetier then me and she says i look ugly!!! shes not a lil kid she is 12 and im 15!! if i ask her to do something or help me clean my she says that i treat her like my slave!! i be nice to her friends and i be nice to her and help her out in stuff. and if she gets made at me she hides my very important stuff some where i can't see... she hidded my book report one day and i really worked hard on this and i got a F because she hidded it and i found it 2 days later when i was looking for it nonstop!!.. because im stronger then her my mom says im hitting her and im the mean one here!! my mom supports her and i really don't wana deal with any of this!! pleaze tell me a way to ignore her and move on..she fights with me for the computer too and every one thinks im the bad one!!...i really can't deal with this anymore!! it is like war bettween me and her!!!!!!! my email- sreedamarla@yahoo.com... im giving this because this is the most important thing!! if u don't have any ideas then just give me a nice plan to die!!!