How does the diary help Anne during confinement in Annex?

The following excerpt is cited at the bottom of the text box:

"While she’s in hiding, Anne decides to think of her diary as a friend, whom she names Kitty. It makes the writing easier. Besides, she doesn’t really have a real friend, ‘and that’s how the whole idea of keeping a diary started’, she admits. ‘All I think about when I‘m with friends is having a good time. I can’t bring myself to talk about anything but ordinary everyday things. We don’t seem to be able to get any closer, and that’s the problem. Maybe it’s my fault that we don’t confide in each other. In any case, that’s just how things are, and unfortunately they’re not liable to change. This is why I’ve started the diary.’"