My mother got her green card in dec08. She left for Asia in March08 and plans to return in Nov08. Since it will be 8 months that she will be out of USA, does she need re-entry permit?
There is some error in your facts. It appears she left in March 2009 (NOT 2008). You cannot file a reentry permit while she is outside USA. If she is outside USA for more than one year, the GC is deemed abandoned. If it is out more than 6 months, but less than 1 year, she can be asked to demonstrate that her permanent home is in USA.