You seem unable explain why she requires a diamond ring, which makes it very unlikely you would be able to change her mind. Engagement/wedding rings are status

You seem unable explain why she requires a diamond ring, which makes it very unlikely you would be able to change her mind. Engagement/wedding rings are status symbols. Most women feel this more strongly than men. When first engaged most women will want the ring to be noticed and be rather conspicuous about making it visible. Many of her friends and colleagues will comment on it and having a high value ring will be a point of pride. It feels good to show off. By saying you don't want to pay for a diamond, she may feel that she will be missing out on all of the pride and status effects. My own tactic for convincing my wife to accept a moissanite stoned ring was simple. Reframe it as the higher status option. The moissanite stones are higher quality and have more brilliance. Moissanite are "conflict-free" stones. We went ring shopping together and allowed her to choose rings/settings that she liked. I pointed out that some of the settings would be out of our price range even with a flawed diamond, but we could substitute a flawless moissanite and people would notice the improvement. Ultimately if she still wants a diamond stone, it is her choice and it is her status symbol.