It is clear to Neith that they would have killed her if she had refused. She doesn’t think they know. Most likely they pretended to themselves that it would never come to that; that Emmett was the last—positively the last—person who would die in this connection. She doesn’t think they know, either, that they still must. They cannot possibly trust her—she will either bring an end to all they know or become like them: rule them, or remove them lest they bring her down.