You have to lose the duel with Cassandra and give her the book once she tells you to call her Mistress, iirc
How do you get the book?
If I remember correctly, you need to do the Berserker questline up to when you enter her mind. Then you can buy it at the shop.
It's only until Julia tells you that she had Ashley "go home" only for you to find her in your room.
Ah, thanks. It's been awhile since I've played so I forgot some of the more minute details.
