I could not find the play that you are talking about in you question but I will try to answer it with some information that could be helpful to you.
Anne Frank did receive her diary on her thirteenth birthday but maybe it was hard for directors to show that in the play, since Anne Frank did write in her diary all of the horror situations that she was experiencing.
It was easier for them to show her diary receiving when she has entered the Secret Annex because the<em><u> bookcase</u></em> was considered as the entrance to the Secret Annex that was the hiding place for her and her family.
