It's really not a lot to ask that she simply avoid delivering killing blows to things that might possibly be related to Yeenoghu's interests and/or the prophecy. xD Any one of us could've told you that finishing the paladin with it was a pretty bad idea.
Besides that, you just got a second attack at 5th level (You did take that invocation, right? Thirsting Blade), so Last Blood is even better than ever. It's an absurdly good weapon for you considering your level, but we can be on the look out for something else.