> A little guidance to people who may be in a similar situation. Just get what she wants.

This is, frankly, very bad advice. If you don't care about the money or your values are aligned with buying an expensive natural diamond, then sure, go for it, but that's not the person who needs advice in this situation anyway. Arguments over money are a leading cause of conflicts in relationships. Failing to address a disagreement on a large purchase like this and the underlying values that cause the disagreement are quite likely to cause conflict in your marriage.

Personally, if a potential spouse felt strongly that an expensive natural diamond was necessary, I'd consider it, but I'd need to hear some good reasoning. In the absence of other information, wanting an expensive natural diamond indicates to me a very large mismatch in values between me and the potential spouse, and I'd want to understand that mismatch before we commit to sharing finances and teaching children our values.

I don't view this as "fighting her about it", either. It's not me versus her, it's us trying to gain a better understanding of each others viewpoints and using that understanding to assess our compatibility.

>> " I think she was very worried she would be judged by other women for not having (or being worth) a "real" diamond. "

> Your projecting your own ideas on her.

Alternate theory: maybe he talked to his wife and she said that. It seems that you're making a very large assumption that the poster hasn't talked to his own wife about this.