Since you are interested in Columbia and your Mother has been deemed not a surgery candidate, have you considerred looking into the trials for the percutaneous valve replacements? I don't know if she meets all the criteria, but it might be worth looking into
http://www.clinicaltrials.gov/ct2/show/NCT00530894?term=sapien&rank=2
Cloumbia is one of the investigators and the docs involved are United States, New York
Columbia University Medical Center Recruiting
New York, New York, United States, 10032
Contact: Martin Leon, MD 212-342-3617
Contact: Craig Smith, MD 212-305-8312
Principal Investigator: Martin Leon, MD
Principal Investigator: Craig Smith, MD
IF she isn't interested in the trials, I'm sure they could recomend the best surgeon. I probably would also look at some of the hospitals in Boston if you want more opinions like JKM suggested. Many centers will give 2nd op from the records/cds of tests and the patient doesn't have to travel.