Theoretically, you are not meant to drive on an international license under the whole "IDP" scheme. Realistically, it's a non-issue.
Washington: I contacted the Dept of Licensing and they said I'd have to apply for a driver's license within 12 months.
Your biggest issue has not yet been mentioned:
Your partner may be covered as an OCCASIONAL driver of your vehicle. Insurance may deny or attempt to deny any claim by reason of the fact that your spouse could be considered more than occasional, and hence need to be added to your policy.
And therein lies the hiccup. I have not come across a single insurance company, with the exception of one (can't remember, will edit when I get home), that will do this WITHOUT a US license issued.
Therefore, you should be aware of the very real possibility (less likely before marriage, very much more so after) that your partner will effectively be uninsured driving your vehicle.
This was quite a scary prospect for my partner and I. Not so much so when it was her `95 Honda Civic I was driving (not discounting the third party/injury potential, etc), but when we bought a new car. Some of my most careful driving ever, and an immediate license appointment was made!