@Avernite
The point about the Korean kid was a distraction and I shouldn't have used it. My apologies. Kim is responsible for her death. Harry's responsibility falls around not recognizing that his knowledge is much more dangerous than Calculus. Either commit fully when you choose to train someone, or stay in your tower.
I think he does know that his knowledge is much more dangerous than calculus. That is why he he stopped giving her information once he realized she was going to use it. The thing is we know nothing about the relationship Harry and Kim had before this. She was a friend, but there are the people you know, and the people you are very close with. He gave her pointers from time to
time, he called her his sometime apprentice, but it is doubtful their relationship was that close. The
evidence for that, is her lies, if she was close to Harry at all, whether just as a friend or as a sometime student, she would have known he would have busted a gut to try and help her, even back then.
Agreed, Harry could have handled it better, but would it have changed the outcome? The person responsible is Kim because she lied. Or take it back further, the real ones responsible were the ones who sabotaged MacFinn's circle in the first place. She was in the movement that MacFinn was the champion/benefactor of, now how did he know about her talent? And how did she know what he was? That has never been made clear. Did she over sell her talent to him? Did she tell him that she knew a guy who could help, but MacFinn didn't want anyone else brought in? Either way, this whole thing reeks of pre-planning. Again the one responsible for her own demise, is Kim, she may have lied to MacFinn about what her capabilities were, she lied to herself about her capabilities, and she lied to Harry from beginning to end. Her choices.
Don't dismiss the fact that Harry was hungry, he said he didn't have much work, he might not have eaten for a day or two. Not a huge excuse, but it makes him vulnerable, one doesn't think clearly when one is hungry. When Kim is lying though her teeth she avoids his eyes... Okay, Harry isn't disturbed by that, wizards and people with talent don't like slip into soul gazes.. However at the same time, if Kim was hiding something, which she was, the last thing she wanted was a soul gaze.
Harry is being condemned because he withheld vital information... That would be bad, except he was up front about it, when he realized it wasn't an academic exercise, he refused to tell her more and warned her strongly against it. She then had the option of coming clean and telling him why she needed it. That gave him the option on whether or not to tell her everything, or insist on going with her. It is all about choices.
His fourth possible approach was lure her in with more information, make it clear to her why she is not up for the task (a little training should do the trick) and offer to help her.
I think he did make that clear, but he also lacked the knowledge that Kim had, the moon when it rose would be full and a horrible monster would be free to kill if it wasn't contained. She never tells him about that, talk about withholding important information, if anyone is guilty of that, it is Kim! Instead she plays on another weakness of Harry's. "You think I'm not strong enough to pull this off..." Kim is a woman, we know how messed up Harry is with them, in Storm Front Murphy is pissed because he still opens doors for women.. Harry is conflicted because on one hand he is old school gentleman, protective of women, on the other hand he knows a lot of strong women and respects them as such.. My point, this muddies the waters, another trick she tries to pull to get information from him. He doesn't fall for it and again tells her up front she isn't at the level yet to pull such a circle off. Then she stomps off before the argument or conversation goes any further.. Enter Murphy, emergency, no chance for Harry to ponder on what Kim was up to or to go after her to see what she was really up to..
Kim was doomed the moment she agreed to help MacFinn knowing she didn't have the knowledge or training to pull off the kind of circle he needed. Even if she was successful in her deception of Harry and he gave her all the information she wanted, that still wouldn't change the basic fact that she lacked training and full knowledge. She might have gotten lucky and it worked, we'd have a different book. But chances are because of lack of training, the circle still would have failed..
If Harry had refused the sandwich and refused to tell her anything, that still wouldn't have changed things. MacFinn's circle was still broken, he'd be loose, she still most likely would have died anyway trying to fix it.. The whole series is about the choices people make and how they change things or don't.