Something everyone needs to get their heads around is that Kim isn't "the good girl." Everyone in the audience and everyone in the show. At one point (at least once, maybe more than once actually) Howard is talking to her and essentially tells her she should stop being around Jimmy because he's such a bad influence for her and he will "ruin" her. As if she wasn't the one throwing beer bottles off the balcony at people's cars, as if she wasn't running high-end dine and dash schemes. She's not some pure, innocent being dragged down the wrong path by Jimmy, and she fucking hates the implication that she is. She makes her own choices, good or bad, and not one of those crimes she committed is anyone's fault but her own. She is doing pro-bono work not because it's her only choice, far from it, and not because she has some sort of pity for the poor. She's doing it for her own absolution - good deeds to erase the bad. But she doesn't regret what she did, she's not ashamed of it, she only wants to balance the scales of justice when she is judged in the end. She doesn't just want Howard out of the way for the money, she wants to punish him for being a sanctimonious prick. She wants to make him hurt because him implying she doesn't have her own autonomy hurt her, and she is having none of that. No man will ever have that power over her again.
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"If you ever feel good about yourself, just look on the Internet." - Ryan Reynolds