@DMSchmidt From what I recall reading, both males and females use "ore" (or "ora") in the Touhoku region of Japan. I think that's where the "-ppe" and "-be" suffixes are from too. TVTropes has some useful notes on it, you could maybe look it up there.
I looked this up. While the use of "ore" for both men and women did die out toward the end of the Edo period, this primarily true of mainstream Japanese. Apparently, this use of "ore" still survives in some dialects. The use of dialects is much more prominent among the elderly, especially things like that. So it is highlighting her age as a (reincarnated) grandmother, just not in the way you thought.