Annoying cousin... What do i do?!?

I am now in vacation in my hometown and I�m staying with some family members. One of them is my cousin Sofie. She may be only six, but she�s definetly a handful. Ever since the first that I started staying with her for each summer vacation (3 years ago) shes been the meanest thing to me. She bothers the f*ck out of me and I sometimes try to be nice to her but she takes it as if im bothering her then tells her mom about and she creates this big deal and its soo annoying. I�m much older than her but I still cant help but feel so mad sometimes. Ive never met such a little b*tch even though theres times where we do ok but thats kinda seldom. I know its definetly not only her, but its mostly her. Shes always giving everyone attitude and always getting mad at ppl for no reason, even when she makes new friends. I feel bad because I think she�ll suffer in the future with that behaviour. I just need some help on how to ignore her or something even though I tried that and its just not working...