When Anne begins her diary, she is a bright-eyed thirteen year old. She like boys, loves school, and loves, spending time with her friends. Upon their arrival at the annex, she is hopeful and optimistic, but over time, you can see that hopeful optimism disintegrate into loneliness, isolation, and deep thinking. This very young girl, who entered the annex a bit silly and definitely hormonal and was quick to challenge and argue with the other residents. She also falls in love for the first time.
Lastly, you might want to address the relationship she had with her parents. Anne was a daddy's girl..... she fought with her mother in a young, teenage girl's typical fashion. Over time, she comes to appreciate and understand her mother.
A possible meaning of the metaphor would be very disappointed because "dirt disappointed" is not meant in a positive sort of way. If you're dirt disappointed it most likely means you are very disappointed, possibly aggravated. Hope this helps
