What are some political philosophy books written by Ayn Rand?

I have to write a 4000 word philosophy essay. I thought that I could do something related to individualism and the government (specifically democracy). So I thought that Ayn Rand would be a good philosopher to explore for this topic but I can't find a book specifically about the topic I want to research. I want something non-fiction (no Atlas Shrugged of Fountainhead please!). I tried to read "Capitalism: the Unknown Ideal" and from the first 7 essays only the first couple were actually philosophical. The rest were more economical. So can anyone who is an expert on Rand recommend me a non-fiction book for my essay?