I’m pretty confused.

Kristen immediately go to the phone after her tryst w/Brady and the smirk on her face I have no doubt it’s part of her plan. And I would not be surprised if she’s had all her “victims” tailed and thus knew Brady would be listening.
IMO Days did not bring Kristen back to be a good person.

she was planning on using Brady exactly for the purpose of it getting back to John and Marlena; thus, her facial expressions showing her sheepish grins and smiles while looking over his shoulder, even when they’re in bed.  She knew that when Marlena opened the door and saw her and Brady (and Kristen did see her), that her plan was working, because she believes Marlena will go straight to John, causing a huge riff between John and Brady, as well as Marlena.  That’s been her plan all along; but, now she may just be starting to have real feelings for Brady now that they have become intimate.  Either way, John has shown no interest in her sexually or otherwise, even though he is stupidly falling into her trap of simply seeking forgiveness.  It’s going to be interesting to me when the bottom of this falls out.  Let’s just say I think Brady is going down the same path where at first he was going to use Kristen in the exact same way he’s using her, but now he might be beginning to have genuine feelings for her as well.  It’s a mess that could blow both of them out of the water once Stefano comes back, because I don’t think either Stefano or E.J. he will approve of this pairing.