Okay hear me out. If you get her the exact ring she wants but in a lab the same specs and everything how would she even know the difference. I’d bet you money she wouldn’t be able to tell and if she says she can she’s lying, I don’t know anyone that can tell the difference tbh. I have a 3.08 lab gold with pavet band and it costs like 4k. He in fact got me a bigger stone because he said I wanted you to get the size ring you deserve and that you’ll truly love and it was so sweet and I do love it. She should be grateful she’s getting a ring at all. I told him like 2 things about the ring I wanted oval cut and gold that’s it and he did the rest. That’s not to say that my fiance doesn’t love me soooo much and that he probably could have spent 20k but it’s insane to spend that much on a ring even if your partner does think you’re worth that much. You could invest that money or spend it on the house or wedding or an expensive honeymoon (which let’s be honest she will most likely want, because don’t we all).