If you could not find her in the censuses, maybe she remarried. If Catholic, the Archdiocese of Detroit records are on microfilm at the Burton Historical Collection (BHC) of the main Detroit Public Library. You have to research in person or hire a researcher, although I was told at one time that the staff would do some research for a fee. I did not verify that, though.
http://www.detroit.lib.mi.us/featuredcollection/burton-histo...Do you know where James is buried? Have tried to see if she is buried there also? Did all of her children live in the US? Have you checked all the censuses for them to see if she might be living with one of her children?
Try the Irish Society of Michigan-maybe they can help.
http://miigsm.org/