With the Kongamato I never got anywhere, we didn't do any divinations or anything, I was just rebuffed forever.
As for when the time is to decide, that would be either when the war is over, when Lanna is dead, or when we have Lanna captured.
Either way there should be one clear decision, we use divination and interrogation magic, to determine how trustworthy she would be if recruited, and then decide whether we want to recruit her, if after we have used magic to get all the facts, we decide we don't want to recruit her, then that's that, I accept that she wont be recruited, and don't mention her going forward.
All I really want, is that we actually do that fact finding, before deciding if she should be kept dead.