Why Does She Hate Me? :(?

My cousin that I was basically raised with all of a sudden hates me now. She started going to the same school as I have (I've been in this school since age 4), and the first two years everything was fine. We aren't in the same grade, I'm a year above her and I've known the kids in her class longer than she has. My point is though, that 2 years ago when she started going she would tell everyone how much she loved me, and how great I am. Now, this year all of a sudden she starts spreading rumours about me saying that I'm rude, disrespectful, that I talk about her (which isn't true one bit!!!), etc. She basically acts like I don't exist in school, I always try to say hi to her but just ignores me. I don't understand, what did I do wrong?? The last 2 years, I invited her to hang out with my friends and me because she couldn't make any friends. In November she suddenly didn't wanna hang out with his anymore and made her own friends which was fine until this started happening. My mom and I literally did so much for her and her mom! I just need advice:(