Immaturity may not be precisely correct, but he's definitely not accusing her of incompetence. Irresponsibility, perhaps. He's not saying that she tried and failed, he's saying that she didn't try. He's saying that she's just blindly playing a role, instead of actually acting responsibly, and that it's so hard-wired into her that it's not even worth him trying to correct it. Hard-wired irresponsibility is close enough to immaturity that it's a reasonable approximation.