You literally transmute matter at will, you do not need to fight Killcannon just turn his robot arm into cheese or something. Your nemesis is a villain that you do not need to consider the whole cannot effect living tissue thing for even a second. That is all.
Change his organs into candy, swap is brain for a shoe, turn his bones into liquid, or if she wanted to be humane make his limbs fall off.
She can’t do this one until she herself is pretty close to death or other special circumstances.
She can’t transmute sentient beings, due to the mental block, which is why these solutions are talking about affecting matter in or around him, rather THAN him