Possible explanation/reason for Mary Shelly's/William's Grandmother

This isn't really spoilers since this happens in the first scene with Elizabeth somehow alive transferring her body to William's neighbor. Just one thing, she DIED in the last movie and has no explanation of reappearing and disappearing. Except this...

Sensing that she and her son/reincarnated husband would fail, she conducted a ritual in which to pass off her powers/knowledge (but not her genetics) to someone else. Of course, that doesn't explain why she waited so long, but let's just say when her power was converted it took Dolores (whatever the neighbor's name is) time to develop her powers. And thus, she finds William, moves next door to him (we never know how long she's been there) and waits.

Very contrived I know but at least better than going with the realization that his grandmother wants to bang him to produce a seed. Yuck