Younger Sibling Issues: She won't admit she doesn't understand me

Hi,

My younger sister has been struggling to understand what my diagnosis of Aspergers Syndrome means to me, and she's been constantly accusing my mum of favouring me over her.

Now, shes 15, mouthy, rude, loud, bitchy, overly emotional and has an attitude problem (all things my friends have told me minutes after meeting her).

I've tried arranging for her to meet with one of the SEN teachers at my high school (I'm 18 and leaving this year) to try and have things explained to her properly, because I can't tolerate her presence (I have to restrain myself from hitting her every time she starts being rude to me or to others) and our mum is working most of the time and is too tired to explain properly.

However, when I told her I'd asked the SEN teacher to speak with her about my Aspergers Syndrome, she kicked off (stood up, yelled at me, sounded a lot like Catherine Tate at the time) screaming 'I DON'T NEED SOMEONE TELLING ME HOW MY SISTER THINKS' in front of her friend (who wasn't even meant to be there).

But this is it. She knows nothing about me. At all. I don't let her near my room because of how she sets me off, she starts on me for no reason half the time when I come home from school, she accuses me of being selfish when I won't share things with her after she's broken her version (i.e. laptop) through neglect or leaving it on the floor.....

I just can't make sense of it. Why is she being so defensive? I genuinelly despise her, and all she ever does is seem to hate me back, so why now the sudden claim to knowing me over a teacher who I now trust and talk with, as opposed to the brat I avoid altogether?