Plot twist: Annith is revealed to not really be a daughter of Mortain, which we find out about two pages before she does the horizontal hula with him. She's weirdly chill about finding out she had a bit of "Who's your Daddy?" with a guy she grew up thinking was in fact her Daddy. Her main concern is what her sister nun assassins will think, and it does make for a pretty awkward conversation. To sum it up: "Hey, girls! Bad news! We're not really sisters. I know. Sad face. The glass is half full, though, because I might get to be your stepmom! Fingers crossed!"
You can tell the author is aware of how creepy this unexplored Game Of Thrones angle is because she immediately has a character declare that "Love is never wrong." And that sounds sweet without any context as to what actually happens in the book, but as soon as you think about it for more than a minute, it becomes something that you might read in a NAMBLA pamphlet. It needs just a couple more qualifiers. Something like "Side note: Love between consenting adults, and preferably not adults who are your father figures and also the gods of death, is never wrong."