She'll be somewhat more OK with that line of reasoning but she'll still be like 'who let those three dorks do this themselves' and use her magical B.S. powers to check that they're still alive every twenty seconds

Susan will probably recognize that Kaoru has grown to be less of a jerk but some part of her will always resent the whole May situation. I think her appreciation of Kaoru will depend a lot on the degree to which May can recover from what he did. That said it's not like she's petty or anything (ok no she is, but not with this) so he'll just be treated more or less normally after a while and he can learn ridiculous Discworld things if he wants to...