Has your wife ever had a United Mileage Plus Card? If yes, the CO offer might be good enough since it's away around getting around the one signup bonus rule... and the card won't be offered again when CO goes away.

If she hasn't had a United Card, I'd wait for a 50k-60k United offer (supposedly there will be one in early October for the general public, search around for it).... Chase has worded their CO applications to imply one can't get a bonus for both the CO and UA card if both applications were after a certain date this year (perhaps July?).