Your assignment is asking that you express your opinion regarding Anne Frank's life and accomplishments. In order to do so, you need to decide your feelings regarding the story recorded in her diary and what purpose you think it does or does not serve.
Anne received the diary on her thirteenth birthday, not long before the family went into hiding. As a result of that timing, the diary becomes Anne's record of her feelings, experiences, concerns, and the hopes for the future that carry her through her involuntary imprisonment in the attic.
It's really a wonder that I haven't dropped all my ideals, because they seem so absurd and impossible to carry out. Yet I keep them, because in spite of everything I still believe that people are really good at heart.
Her life's accomplishment is providing insight into the reality of that situation and showing how to maintain a positive attitude in the face of extreme adversity.
I don't want to have lived in vain like most people. I want to be useful or bring enjoyment to all people, even those I've never met. I want to go on living even after my death!
You need to determine if you feel she accomplished her wish to be "useful...even after (her) death."