Thanks again for all the great advice all. I did some research today and I found two companies that seem very aligned with my values here: GreenKarat and BrilliantEarth. While I'm trending more away from consumerism these days I don't mind spending money when I can support companies that give people more earth- and society-friendly options. I just would never want to support slave labor, torture, the financing of wars, etc. with a purchase as sacred as this.
I'm going to keep looking and see what I can find. I may even take up the advice of not buying a ring at the time of the proposal and instead going together to buy one. It might not be quite the "fairy tale" that you see in the movies but it's important to me that what I do here is both something consistent with my values and also something that makes her happy.