“He didn’t say who he was writing to.” Effy stared down at the page again, just to be certain. “He said she had a Southern name . . . one of Blackmar’s daughters. Myrddin’s diary mentions that Blackmar’s eldest daughter showed him some of her poetry, remember?”
So she did notice that. Why didn't it ever occur to her to follow up with the clue, then?
Because poor plot contrivance 😑

