If it is any help, an Isabella Macartney was born to Matthew and Ann Macartney of Cromkill around 1898. This is the family in the census record above. Your Isobel could be a daughter or niece of this one. It is very common in this family for members to be named after an aunt or uncle. Matthew did have a son Matthew who was born around 1892. Perhaps he was married to Margaret Jane? Incidentally, if her maiden name is Hanna, one of Matthew's sisters married a Hanna. Again, not uncommon in those days when travel was limited. Thanks.