What to do when your sister tries to steal everything you have?

she's 4 yrs younger and has recently stole my best friend.she always needs to be the center of attention and does everything to get it.i feel so sorry for her and ive always stepped back and let her have the limelight.but i cant stand it and have broken ties with her completely,we live in the same house and it's hard,she's apologized but i can't forgive.