where can I find immigration for my great grandmother

Where can I find immigration resource for my great grandmother? She came through Ellis Island around 1912. I know that my great grandfather came the U.S. before this several times back and forth from Italy. My great uncle was born in Italy and was 9 months old at the time she came over. Not sure if she came by herself or with my great grandfather. Any suggestions on where I can I find this on a free website?