How should i handle sibling abuse?

hey i am 19 years old girl and i have a younger sister who is 15.Now a days she has become very violent towards me.like if i say somethong rude she comes and beats me.I asked her many a times why do you behave like this,i am your elder sister,you should respect me adding this also that i never beat you or slap you for small things then she says that who wants to respect a girl like you who puts every person to depression.Last night i was having fever so i told my mom that i don't need fan,when i slowed down the fan & took out the terminator she became very violent and started hiiting me very badly without thinking that i am suffering from fever.Then after that she started studying loudly to disturb me from sleeping,when i got irritated then i threw a pen on her and told her rudely that if you want to study go somewhere else, then she came and sat on my back an started pressing my neck,suffocating me,pulling my hair and twisting my arms and started saying that today i'll kill you,then i shouted for help after that my father came and he was very angry.She said that it was all my fault and i was hitting her very badly.I felt so bad that i just kept quiet.This has happened many a times,she always blames me that i only start a fight and not she.When i was at her age i also use to hit her but not so badly.i am not saying that i never slap her or beat her,it's just that when she is very rude i just give a bang on her back,i rarely slap her.once i also pressed her neck and suffocated her when we had a big fight and she too but i said sorry after that because i felt bad and promised myself that i'll never do so again but she never seemed to be sorry for anything.Now i don't want to talk to her also.I just want to talk her and tell her that now our relationship is over and we shoud walk our own way without bothering about each other anymore.She is so shameless.I don't want anyone to know anything about it not even my college friends who are personally very close to me but if she says anything to anybody and blames me then i will not keep quiet. Seriously speaking now i am afraid of her.I am scared if she goes and tells her society friends who are mine friends too and school friends then she'll blame me only because she never see what wrong she has done and she blames everything on others.Once she also abused our mother.She behaves like the sweetest person on earth with her friends and she is very difeerent at home.I want to tell her friends what is she in real and how she behaves with me and her family mothers.It's not that she's never sweet with me or parents but when she behaves violently i don't care about how sweetly she was yesterday.We have a 7 year old brother also.Sometimes when he behaves badly with her or abuses her she slaps him very badly and when i say that when you don't respect your elder sister why do you expect him to behave properly with you then she just says shut up.Whenever everyone is asleep at afternoon or at night she puts on tv on high volume and watches it but if she is sleeping she needs complete silence.Because of her behaviour towards her elders is drawing hatred in me for her.She is very dominating at home and very sweet with her friends and if i tell this to my society friends they will not believe this because i don't talk to them much as they are of her age.Even the ***** word is also less to define her.She beats me like hell and i am speechless because mom and dad are not saying anything and even if i go and tell my mom about this she is like this is between you and your sister i'll not do anything.Now a days i am feeling very depressed not feeling like doing anything or going out.I want to tell everything to someone who can help me out but i don't see anyone around.I want her friend's to know how she treats me and her elders.It's like i am at the edge of my life.If she goes and says all lies to society friends as everybody knows me down then what will i do.I want to tell one of my society friend from that group so that they can know what she really is,should i do so because if i will not tell them then they will have bad impression about me and then no one will talk to me which i don't want because then i will be left alone?and how should i control her from beating me and abusing me?please suggest me how to handle everything because now i am blank and if i will not control it now then my life will become miserable.HELP ME please!!!!!!!!!