Legal Permanent Resident of US

Situation: My wife (Canadian Citz-US LPR) and I (US Citz) have been married for 12 years and counting. She has worked going on 12 years in teh US alone (15 in Canada). She is almost 59 and is looking ahead to qualifying for SS. Im reading a few things that are not quite clear such as "you can file for the first 5 years that you worked" and things similair as that. Regardless of all the confusing chatter, we want to knwo the facts and bottom line. Will she be fully elligible when she reaches the majic number (assuming current law). I also have read bits and pieces about credit sharing with her former spouse in Canada. Is this mandatory? Does she use mine as well even though I wont be retiring anytime soon? anything usefull along these lines are most welcome. Thank you, Oscar