You might consider waiting for her at the boarding area for the ORD-SEA flight. This will give you a greater margin for error in case your SEA-ORD flight is delayed. It will also prevent the possibility of missing each other in the international arrival area (low probability but has happened before).

The upgrade is still up in the air, but when you get to ORD you might want to check with the GA if they can put the two of you together, they normally keep some seats under airport control.

Good luck,