1. If she is a US citizen, the term "non-resident alien" does not apply to her. No matter where she lives, she cannot be a "non-resident alien" because she is a US citizen (not an "alien").
2. Her mailing address is where she wants the IRS to send any correspondence related to her return. Her home/permanent address can be wherever she considers her "permanent address' to be.
3. You do not have to convey to the IRS that you are living abroad - just comply with the filing thresholds, whatever they are for you. The IRS will only bring up your physical location if they have a question about what you filed on Form 8938 or something else on your return.
4. The IRS does not "expect" and is not "looking for" a reporting threshold; they expect you to comply with the reporting thresholds. They are not examining addresses to see if they indicate a different filing threshold for Form 8938.
