Considering that the annual fee is $450, you're still paying $150 more than what you get in annual credit. Granted, you get other perks associated, like Global Entry fee and free award night after first year, but a lot of the other perks aren't really valid if you guys travel together already (not like she needs status when you guys are already traveling together). If you are gunning for the 100,000 points, then sure $150 (or $50 if you factor GE credit) is a nice way to get a couple nights for free.
Personally, if you don't need the signing bonus, there's not much of a reason (certainly not because of $300 annual credit).