Why does she flirt like this?

This girl I like keeps dropping hints that she likes me. She says things like I have been dreaming alot about you and even asked if I would take her out to her favorite resturaunt. We write notes to eachother (nothing heavy like "ilove you" or anything) i'm always a little flirty in the letter but it seems that every letter i get from her, she just talks about her day and random crap lol i want her to be flirty like she is when i talk to her! why do you think she's like this?