I just don't see a logical incentive for her to come clean, I don't see her having sympathy for anyone but EG, so I can't see any point of appealing to that?
I hope you're right about that tactic being sufficient for her, but....that was probably used in the pre-arrest interviews and it's probably already failed.
If some of the mistreatment of Lucas is about punishing JH, and she has a history of these major primal blow outs followed by equally passionate make-up sessions....where she regains control and goes back into planning, manipulation and self-protection mode. Primal rage is the only thing I can see that can get her out of the latter state of mind? What incentive does she have to do anything for Lucas right now, anything for JH, anything for Lucas' other relatives? If she walks out of jail she has all of this to hold over him, she can't tell him, but she knows inside what she's done to him, and she gets to comfort him and to reiterate that it was "them", "we'll hate them together forever, we'll be closer forever because of this incident, you, me and our baby."
If he is not complicit in abuse, then if he's coming around to facing up to her about it and kicking her out over it, then maybe her getting out is the best option to set up a fight between them that will send her into 'primal rage' (I've made that up, I don't claim it to be a technical term.)
I hope they've got a good handle on her and can get something (by whatever method, I don't demand to be right, I'm just conjecturing in my head and typing out my thoughts) before someone posts bail.