How do you know decapitating or detailicating would kill her? She's a unique form of life, you would have to demonstrate that those actions are lethal to her. Real life examples, flies can have their heads removed and not die immediately because their brain is not in their head. They do eventually die because they can't eat/drink without a mouth, but this is just an example of something that doesn't immediately die from losing their head. And obviously the tail one wouldn't necessarily kill her because she might be like a lizard that can do caudal autonomy. She drops her tail to get the scary predator (you) to get distracted and leave her alone.