Any tips on how to help my little sister?:)?5 STARS!!!!!please help!<3?

Well my sister's 9 years old ( In year 4 ) And there is this other little girl that she used to be friends with but as soon as my little sister stopped hanging around with her and playing with other people the other girl decided to make Abbi ( My sister ) Feel as bad as possible so, when my sister got put in to extra tutoring for maths class Lola ( The girls name ) picked holes in that saying that she was in top set and that maths is easy ect... She then got this boy that my sister ' fancied ' ( you know how they are ) And told him to keep saying horrible things to my sister. Then when Lola got a valentines card from her relative she brought it in to school and told my sister it was from the boy that my sister liked ( They both like the same person ) The bottom line is I think Lola is jelous of abbi as Abbi is very pretty ( I wish I looked like my little sister !) Abbi has blonde hair big blue eyes slightly tanned skin, she's like a child model to me! the other girl has brown hair and is rather dull in all her photos, she has everything. She has a laptop, facebook, Smart phone, Only child and she is the same age as my sister. My sister constantly feels miserable coming home from school and thinks that learning means nothing to her, she still reads picture books ( I was reading 400+ page hardbacks by that time ) We havn't tested for dyslexia but I dont think she has it she is just reluctant to try it. Please give me some advice she refuses to let me help her?!