Kayla's mentioned that she sees herself as worthless (because she stays in bed all day strung out on pills and watches Star Trek The Next Generation) and that Nick is a hero for doing the housekeeping and looking after the kids for her (at some point, he clearly stopped, though) while also being the breadwinner
Nick got a tattoo saying "I will be us" aka she's a bad parent and Nick is carrying them (he tries to play it off as a romantic "I'm here for you no matter what" thing, but it's obvious he's trying to play into her beliefs that she's useless and she's blessed to have Nick). His strategy is to make her feel like she's useless with a ruined body and that only Nick would ever even tolerate her, let alone love her.
I could easily see Nick telling her "I've been strong for us for our whole marriage, now it's your turn to be strong. You have to go to prison for us. It's the only way. If I get locked up then we lose everything." and she'd believe it because she's a mentally ill pill head.