I think it's fine if she wanted a different style of ring, for the same budget. It's another thing if her complaint was that the diamond wasn't big enough or high enough quality. Ultimately, it's she wants what she wants. If I were the groom, I would be wary of my fiance if she said, "take it back, spend more money", particularly if I had already cost me a lot of money. I would begin to question our financial compatiblity.