Well, that must mean nearly everyone is okay with murder, right? I mean, a lot of heroes, anti-heroes and antagonists outright murder in fiction. Heck, Lolita is a classic. If your logic of wanting to do what protagonists do is correct, all literature teachers would likely have been incarcerated by now.
What makes you think she is not just mono, that she KNOWS what she wants? What makes you realize she might be open to the idea, rather then being unable to detach herself from someone she cares for so cleanly?
As for the sex? I'd advise not pushing it. You won't win much sympathy from her for asking her for it. Let her get comfortable first.