The jewelry purchased in the US, exported to China, and then about to be reimported into the US, ought to have been declared when your wife exported it from the US. She would then have a stamped form to present which would demonstrate that the items were purchased in the US. But, it is too late for that.

She should have with her the receipts for the more valuable items which will presumably show a US point of sale and simply be prepared to acknowledge, if asked, that she did not go through the process on departure. It is highly unlikely that CBP will take any action should it even bother to ask. In the event that it does, so long as she has declared the items, bear in mind that the duty will hover in the 2% range. Thus, on a $2,000 item, the duty is $40, so not some devastating sum and one which one might recover later. The only real mistake is to fail to properly declare because that is what leads to stiff penalties and time delays.