Anne Catherine Emmerich, a 19th century
German mystic, claimed to have had revelations which told her that the parents of St.
Anne (and so the maternal grandparents of the Virgin
Mary) were named
Eliud and Ismeria.
I haven't found yet whether the name Ismeria was ever mentioned before
Emmerich's visions. But I would imagine your great-aunt got the name because of the idea that Ismeria was
Mary's grandmother. French Canadians seem to have been particularly interested in giving children names of obscure saints back during the 19th century.
http://www.spiritdaily.net/emmerichmarylife1.htm