Re the bag... the rechecking is immediately after customs before you exit. Unless you want to break the surprise, you aren't going to be able to recheck it. Other issue, I'm assuming you're going XXX-ORD-SEA. You may not be able to check a bag easily at ORD.

As far as where to meet... her flight will arrive at T5. Among the possibilities is to wait for her where you board the airport train. Just one idea.