If you decide to turn on her after you convinced her to stand down, the Runepowder always explodes now. Was something changed, or is it bugged?
That didn't happen in my other 2 playthroughs. I was always able to convice her, then turn on her, she'd try to run and I was able to kill her no problem.

Honestly I'm having so many bugs and annyoing inconsistencies with this game, more than any game I've ever played. Not even a Bethesda game...