Little Sister issue.....?

For years I've had to put up with her.

But now that she is 12 and going through puberty her b****iness has gotten worse.

I am 15.

Always has to have her way.

Now I am trying to live my own life and do my own things like study etc and I am forced by my parents to help her whenever she needs it for her work.

When obviously me being in grade 10 my work is a lot of my important than that of a mere grade 7er.

For instance today

She was being her usual rude self and I so happened to own her verbally.

So I didn't talk to her for the rest of the day.

She needed help with her work and mum told me to help her.

I said as long as she apologizes for being rude.

I get yelled at and get told to leave it and she'll do it (she can't so she asked my brother than finally my father)

I'm sick of this.

She always gets out of work and when she can't she annoys me and works extremely slowly. Which I explain to her that we'll finish quicker if she hurries up.

She tells mum I'm telling her what to do and then my mum proceeds to tell me that I am not the dad and that my sister can stop working for me trying to take control.

So it's just me and my brother working outside for another hour and a half....

Whenever I approach my parents I get told off for being a smart ***.

Just I can't stand her. What can I do