Propose with a simple gold band, and then upgrade her later to a recycled, conflict-free gem from a conscious, reputable jeweler, if she wants that. Talk to her after the proposal to see how she feels.
My husband proposed to me with a gold band, which I loved, and still do wear. I'd made it clear well in advance of his proposal how I felt about 'blood diamonds' or 'blood sapphires.' Our wedding bands were also simple and made of conflict-free materials. I agree that the whole 'diamond as reflection of penis size' is ridiculous. You can buy crappy, big-carat settings at Costco and Fred Meyer. It's no true reflection of wealth, status or degree to which you're 'loved'.
It's tough to track down where a gem was obtained unless it's synthetic. Go with the basic gold first! Good luck.
