I think Janine is Moriarty’s sister.
The most obvious support to this is her accent, they’re both Irish. But they both act very similar around him. Her veiled threat when she left the hospital room about how he’d regret treating her how he did and that they could have been friends just seemed very Moriarty-esque to me.
Plus with that twist at the end!
IT MAKES SENSE HE HAD A FUCKING GOD DAMN BROTHER IN THE BOOKS.