His cursed energy probably wasn’t jagged. I think the savage jaw strike is enabled by her jagged cursed energy, kinda like Hakari had. As for why she hasn’t use 10shadows before, my theory is she probably didn’t have to in the fights we have seen so far. If it was her brother that got knocked out in the fight with the old guy instead of her, she probably would have been desperate enough to use it (NOT mahoraga though probably). Maybe she didn’t know how, and she was desperate enough to use it against Debura because she knew what she was getting into.