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.
Maybe since starting using her powers, she has pigeon holed herself into her current, much weaker fighting style, that isn’t so taxing on her. It’s like those psychological trick videos in which the host trains random people and viewers into solving some problems in one particular style, and then when they are presented with simpler problems, they just default to the more difficult method and don’t consider anything else. She’ll need to learn fighting again with her full skillset.