What is wrong with her?

I love my cousin to bit, she was really nice to me and she is really pretty.It was her birthday yesterday so i wished her happy birthday today and she just put thanks but for everyone who wished her happy birthday she put kisses. Every time i talk to her now shes really rude.Shes 16 and im much younger than her i don't know what happened but then my other cousin who's the same age as her knows her but she didn't know me and her were cousins and since she found out she was like oh shes my cousin to, even though she isn't and she like her more than me.They are both being really mean and ignoring me all the time and same i pester them but they don't care when there friends to talk to them all day everyday.It makes me sad :( What can i do??