Why Doesn't She Mind Her Own Business?!

Do you know what really bothers me these days?Well it's when my eldest sister never minds her own buisness! People that has older brothers or sisters might feel my pain...
Whenever I am doing Facebook in my freetime, she would tell Mama that I'm not studying. Right there is when I want to kick her out of this world. I mean I can handle all the things she does mean to me but not when she is minding MY buisness!!!NEVER!!Also she would act as if she is mumbling, and say I'm stupid, and that I get 'F's! Does she even know what she is saying? I hate it wheh she mumbles to herself. If she wants to mumble, go somewhere else rather than my room!!!
I still remember when my sister would go on youtube and watch movies, when she was suppose to study! I never say anything. See? I am not minding her buisness! That's her life, not mine!
I sometimes think, does younger sisters get to say their own opinon about something? Or is it only the eldest who says whatever they want? I want to go up to my sister and say she can't say I'm stupid just becuase I am doing the internet. But I don't dare because I know what would happen next.
What I am telling you guys right now is that the eldest sister /brother has to mind their own business and don't leave a stressful day to your younger sister/brother.