I read my sisters diary and am now scared?

I know I shouldn't be reading my sisters diary but I found it in the living room last night. It was big and had "Twilight" Written across it in big letters. I'm scared. Throughout this book she refers to herself as 'Bella' and she seems to be infatuated with this guy 'Edward'. I'm afraid this edward guy is not right for her! He seems to be abusive and glittery. She also is VERY obsessed with him! Could this be a mental disorder? She wrote another diary called 'Harry potter' 'm reading that next.