BM dying makes sense. Its implied her durability comes from haki. It deactivates when her mental state is weak and whereas Law needed to struggle to negate Doc Q's powers, BM was casually and effortlessly able to negate Law's powers.
imo BM was out of haki by the time Kid landed the second damned punk.
She was getting damaged by the bombs in onigashima, that first explosion wasn't even that big.