I've decided that while Plague tried to be a good mom (by her standards) the way She was raised heavily influenced the way she raised her kits.
She Scarred both girls with a little cross on their foreheads to mark them as her "heirs" (something that was done to her since she was in a position of power in her old rouge group), and was pretty emotionally abusive and physically negligent. She never hit them (she has a no hitting kits rule, despite what she did to Wasp) but she told them to "play" (train) with their claws out . She also didn't stop Usula from wailing on Banshee all the time, because she was the "stronger" child who would have taken Plague's place in the old rogue group.
All this leads up to when Banshee finally leaves, Plague strikes her for the first time, clawing across the cross scar as her way of disowning Banshee.
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DUDE