Younger sister a jerk- quick help please! 10m pts!!?

so my twelve year old little sister is always misbehaving like a jerk around me and my friends. she keeps telling people that i am so boring and serious that i can't get a boyfriend, like that's any of her business. she's too young to even talk to me in a disrespectful manner but she abuses me all the time. my parents are stupid, they don't say anything to her whatsoever. i feel that they are afraid of her, just like everyone else. i suspect that she has some mental instability but no one agrees to take her to a doctor because we live in a small town and , well, word spreads around. i am sick of her and now i am even forced to sleep in the same room as she. she stinks and kicks me every night and my parents are like blind to everything that she does. they Always expect me to be the bigger person which is not possible. after all, i too am just 15 years old and she's making my life hell. ps i never had a childhood because of this dumbazz sister of mine