Your mother-in-law will be presumed to have abandoned her residence. It does not matter if her green card continues to be valid. Any stay outside the United States of a year or more triggers a presumption of abandonment. Your mother-in-law could apply for an SB-1 visa at the U.S. Embassy. To be successful she will need to thoroughly document her medical condition and establish she did not intend to abandon her status. The other option would be to have a new immigrant visa petition filed on her behalf.
Answered on Feb 24th, 2016 at 3:58 PM