The first part is easy, yes she can absolutely leave for vacation. For how long depends. From the USCIS website:gavinmac wrote:Can she leave during the two years for vacations, and if so, for how long?
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Abandoning Permanent Resident Status
You may also lose your permanent resident status by intentionally abandoning it. You may be found to have abandoned your status if you:
•Move to another country, intending to live there permanently.
•Remain outside of the United States for an extended period of time, unless you intended this to be a temporary absence, as shown by:
◦The reason for your trip;
◦How long you intended to be absent from the United States;
◦Any other circumstances of your absence; and
◦Any events that may have prolonged your absence.
◦Note: Obtaining a re-entry permit from USCIS before you leave, or a returning resident visa (SB-1) from a U.S. consulate while abroad, may assist you in showing that you intended only a temporary absence.
•Fail to file income tax returns while living outside of the United States for any period.
•Declare yourself a “nonimmigrant” on your U.S. tax returns.
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Note that there are steps to take, which would only be necessary for long term absences, such as maintaining a bank account, telephone, etc. in the US during the temporary leave of absence.