Growing up in Montclair in a neighborhood of Irish immigrants, Barbara Williams disliked her grandmother. But it wasn’t until much later when she learned about the history of her ancestors that she began understanding why her grandmother could be so difficult to get along with, leading the way for Williams to turn that resentment into empathy.

That was the basis for the Barnegat Township resident’s new book, I Hate You, Mary Sullivan: A Memoir of Inherited Trauma, recently published by Cape House Publishing,…