I believe it is B. One. The “her” is talking about “one” of the sisters.
Answer:
The main idea of this text is about how at one time, Man did not know about fire. Fire was introduced to Man by nature.
Explanation:
The simplest ways is to use euphemisms. Doing this we make things seem less important and less emotional. For example, when talking about wars, many people have difficulties to say things like war crimes or civilian death so they use terms like collateral damage or casualties.