You have some excellent questions but the answers are generated by information not contained in your fact pattern. The most critical issue is why you're living abroad and how much time she has spent in the U.S. These will drive the answers on filing the I-751, the filing and re-filing of the I-131, her ability to naturalize (and thus remove immigration entanglements) as well as tax issues and abandonment issues. Best to retain counsel and fully develop the facts so a carefully considered response will help direct you accordingly.
I agree with Mr. Eichorn. Plus, she should be filing an N-470.
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