Queen Elizabeth is an important part in England's history; she had such an interesting life from before she was Queen to when she ruled, also she did many remarkable things while in power.
These are all true, but they are obvious. When you give a speech or essay, it's because you have something new to add to a discussion among people. So, your task is to make an interesting observation.
Sometimes it is interesting to compare her to someone else.
Sometimes it's interesting to come up with a word that perfectly describes her, and that word becomes the theme of your essay.
Look at interesting articles that have been written about her, and you'll see that the best ones have something that makes them (the article) unique.
All you have to do is read and read, and you'll come up with lots of great ideas about her. You can do it. You could even do it if it was college work. If you read every day you'll see that it is not that hard!
:-)