This question is in regards with my mother's Green Card. She received her Green card in Dec '06 and after staying here for a sometime, returned to India in May '07. From what I have read about keeping your Green Card current, she has to be back in the US before the end of one year from the day she departed the country. However, someone mentioned to me that the first time you have to back within 6 months...which in her case would be up by late Nov '07. I have read thru her welcome package and online, but have found no information that corroborates that...
Can some one give me any insight on this matter??
Thank you...

Your mother must show proof that her primary residence is still in the USA. She will need a re-entry permit if she stays out of the USA for more than a year. Check the USCIS website for details. Being away for 6 months is relevant only in determining continuity of residence for eligibility to apply for naturalization.