I'm glad to see you mentioned natural law. I haven't read writings by St. Thomas Aquinas. But, long ago, I read John Locke's Second Treatise (which I still have), as well as writings on natural law and its role in the formation of our country.
When I read Atlas Shrugged in January for the first and only time, her philosophy seemed (almost) identical to the philosophies espoused by Locke and others. But, in listening to Rand's interviews, I never heard her credit them. Maybe I missed it, or maybe she credited them in writings I haven't read. But, I got the impression she believed her philosophy was original. She did have an original take on it, that's for sure.
I’ve just finished Locke’s First Treatise, and I’m about to begin the Second.