DC continuity has gotten so convoluted, I don't think Johns understood the nature of "Black" Mary's powers. He made it sound like she had a portion of Black Adam's power, but she had given it all back to him some time ago and her current power comes from Darkseid, at which point she began serving him in Final Crisis.

Between her two stints as Black Mary, she also got her own powers back from the Greek Gods, who bestowed them upon her for her helping to save them from Darkseid's forces. I don't know how Shazam could remove them, and even if he could, how he'd have the right since he didn't bestow them this time.

And boy, dying in comics has gotten really cheap. Just in the past couple of months, we've seen the resurrection of Isis, Shazam, the original Quasar, and Moondragon.

By the way, is this page still being maintained? The comics in the preview pane above dates back to February and it's now April.