I'm reasonably certain no one on this site is going to do this for you, and there are two reasons for that. One, it's important--especially in a speech--for you to speak from some experience and understanding. In other words, to speak effectively, you must speak what you know and believe to be true. Second, this is a broad subject and I have to wonder if any such "ready-made" speech even exists, though people have certainly written a lot about The Diary of Anne Frank.
Instead, let me give you a few ideas from which you can write your own speech. Every good speech is well organized and well supported with examples which prove your points. So, decide what two or three things (depending on how long the speech is supposed to be) you think are most noticeable or recognizable or worst or interesting or whatever else about her writing. Write a clear thesis (purpose) statement including those two or three points. Then, prove it, using some examples from your reading and observation for each point. From there, you have the makings of a speech.
For example, one quality of Anne Frank's writing is that she is honest. We know that because she shares everything she thinks and feels, and some of it is not very flattering. Because she includes __________ and _________ and__________, we trust her as an honest, reliable writer. (You fill in the blanks with some examples, and you've made your argument.)
The only other element to consider, then, is what to do for the intro and conclusion. I assume your teacher has talked with you about the variety of ways to capture an audience's interest and how to summarize and conclude effectively. In this case, perhaps you can choose a short passage of her writing which seems applicable, using part of it at the beginning and finishing it in the conclusion.
Below I've included a link to some critical articles which might give you more insights on Anne Frank's writing style to help get you started.
Best wishes as you complete this assignment!