Which sentence from the story best supports the reason why Anna is writing in a diary

There are many sentences that support this but I like this one best:

Writing in a diary is a really strange experience for someone like me. Not only because I’ve never written anything before, but also because it seems to me that later on neither I nor anyone else will be interested in the musings of a thirteen-year old school girl. Oh well, it doesn’t matter. I feel like writing.