Ann/Anne/Annie Croston

I have been doing genealogy for fifteen years now and still have not been able to find my great grandmother's family. All I know is she was from County Cork and her parents were John and Mary Croston. She came to Boston, MA around 1870 and married in 1872 to a James Graham. I'm not sure whether her parents ever came to the USA. Any help would be greatly appreciated. Some people have suggested Schull, Cork as a possibility.