In many ways, this compelling narrative tells us the story of one girl as she displays courage in facing the hardships of a Jew that is forced to hide her existence in a world where discovery would mean death. In this sense, the very fact of writing a diary at all is an act of courage, as it testifies to a desire to be known and identified for who you are in the face of the secrecy and forced hiding that characterised so much of Anne's life.
In this sense we can see courage as a constant characteristic of Anne throughout her writings. The reference you allude to in your question states:
I'm becoming more and more independent of my parents ... If only I can be myself, I'll be satisfied. I know that I'm a woman, a woman with inner strength and a great deal of courage!
For Anne, to face growing up and going through the teenage years in such a claustraphobic environment must have been extremely difficult. However, what she writes in her diary, and particularly in the final entry, shows and demonstrates that she has gained a greater sense of self-knowledge and understands her conflicted identity as she seeks to break free from her parents but at the same time is forced to stay with them. The way in which she develops a sense of the kind of woman she is slowly becoming shows tremendous courage in the face of significant adversity.