QUOTE(lostinfrance @ Oct 9 2007, 10:11 AM)

Sounds like her main problem may be in establishing domicle in the US.
Actually, I was afraid of this domicile thing, too, having been away from the States more than 15 years and having really NOTHING I could call a real tie to the States anymore except my US driver's license. I did all kinds of things - set up a bank acct, got voting records...and at the interview, the Embassy couldn't have been less interested in that particular question. Domicile seemed to be no problem for them. Of course, it can't hurt to do all that you can. Each case is different and it's better to be prepared than not.
As for the IRS, it really is easy to get 3 years of IRS tax returns done before the I-864 interview. Here, in France, the IRS office in the Embassy told me to send in my returns (1040, filing separately, with 2555EZ) with a copy of each and a SASE. They stamped my copies as proof of receipt and sent them back to me in one week. I took these copies to the interview.
Good luck.
With the issue of domicile, the embassies differ pretty wildly on strictness. Some are very severe about it, and others like Paris and London are pretty loosey goosey.