score:7
If you bought your girlfriend jewelry while she was living abroad, then it is her personal possession. If she comes to the US for a visit she is permitted to bring them with her, just as if she had bought them herself, as long as she intends to take them home with her again. There is no limit on the value, or at least if there is it is well above $10K.
The only issue with that is if customs don't believe that the jewelry is genuinely her personal possessions, and that she intends to import them. (The receipts don't help, as they prove only that she bought them, not that she does not intend to resell them.) This doesn't happen often, as plenty of people bring jewelry with them and take it away when they leave. In some cases it may be worth declaring the jewelry and explicitly stating they are personal possessions, rather than having customs search her and then accusing her of illegally importing. She shouldn't have to pay duty if her story is accepted.
If your girlfriend is moving to the US permanently the process is different, but she should still be allowed to import her personal possessions duty free. Further questions about that should be asked on our Expatriates site.