Ahh yes, Devil’s Due, a properly cheesy old-school style Trek episode. How many original series episodes had lame “gods” with bags of tricks? The thing with Ardra was that she was a real pain in the ass, and as good as her tricks were, I doubt she could’ve stopped someone from phasering her in the back.
Besides, once you claim to the world that you are in fact the Devil, I think you give up any normal rights not to be shot at. I’m somewhat reminded of an episode of Buffy, with some ancient demon that was immune to conventional weapons. . . but that didn’t extend to a bazooka.