Like EC&IC said, sounds like you have a similar situation to us: my spouse and I were living in Canada until I got my residency. My spouse is a homemaker and hadn't lived in the US for 6+ years, no tax returns etc.... We had a joint sponsor. All we submitted to NVC on this regard was a letter from my spouse, explaining that she planned to domicile in the US once I got my residency. Nothing more than that.