(I decided that for the time being, "My Grandfather's new wife" will be a suitable enough title. Step-grandmother sounds odd, and it really does feel wrong calling her my grandmother just yet, even though I rarely used the full word for my Gramma. Gramma was always Gramma, or maybe Grandma at more formal occasions. Thus, saying "my grandmother" doesn't really bring back memories of Gramma to me, because that wasn't really her title after all. hmm...)