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?
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.
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.