You have to remember, Kaine is a man. Men just don't pay enough attention, especially when it's women problems. When I've had mood swings around my husband, he gives me space, and even if we talk about it later, we don't talk for a long time, just enough that we know everything is back to normal and we can move on. My point is, if something were severely wrong with me, I'm sure my husband would know, but I'm not sure how closely he'd watch me or if he'd even pay attention to what medication I'm on unless it's one he already knows about, especially if it's a woman problem. He already doesn't like me talking about a period or women things like tampons or pads. He doesn't even want to think about his daughter becoming a woman. Men don't like to fixate on woman problems, even PPD.
Also, men just want things to be fixed. I'm sure he did watch her, and probably knew she was on medication, and that was the extent of it. He probably just wanted her fixed, probably wanted the problem to go away, and like every man, doesn't understand that some problems can't just be fixed. It takes time, and even with time, there's no guarantee she was going to be PPD free someday.
He probably had the hope that she would be okay and never dreamed she would get to the point where she would harm someone. There's a big difference between someone who is sick and needs help, and someone who would harm someone else. I doubt Kaine ever thought she would hurt one of his kids, and why would he necessarily make that leap?
I'm not going to come down hard on Kaine with something like this. Men just don't understand things like PPD, or PPP, or heck, even PMS, or PMDD. When it comes to women problems, men leave that to the women. Now if it's a man problem, they know all about that and will handle that, but don't want to talk about it.
Yes, maybe he should have paid more attention, and if he was a woman, he would have, but he's a man, and they just don't pay enough attention. Heck, I have to tell my husband and dad when I get a haircut because unless I shave my head, they wouldn't notice otherwise. Now the women in my life would notice if I cut just an inch. That's just how it is with men and women.