You are right. She doesn't need the GC to leave the country, she only needs it to reenter.
Maybe she is thinking of another situation where people do need a visa or other document to leave the US. If somebody was inside the US waiting on their pending adjustment of status (AOS) process to obtain a green card, they need Advance Parole in hand before they leave the US (or a dual intent visa status), otherwise their AOS application would be considered abandoned. But once the green card is approved, that is no longer applicable.
When she arrives at the airport they will give her an I-551 stamp in her passport, typically valid for 6 months. The I-551 stamp is the equivalent of a green card in terms of using it to travel or obtain employment within the US.
But whatever you do, when you send the GC don't send it by mail unless it's going to Canada. Not even global priority mail. Green cards have a habit of getting "lost" when sent like that internationally. Use a private courier like Fedex or DHL.
Last edited by Jackolantern; 23rd November 2009 at 10:44 AM.
PD: Jan 2003 (EB3 rest of world)
I-485 filed: June 2005 Approved: July 2007
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.