As you indicated, killing can be justified in some cases, and in other cases, it can't be justified.
When you consider that every pregnancy is a (usually manageable) threat to a woman's life, we can examine abortions as a means of self-defense. (One of the justifications you mentioned earlier)
In the case of a non-rape pregnancy, a woman and her partner assume the risks for pregnancy. Even with protection they know (or should know) is not 100% effective, they assumed the risks. That amounts to an implied consent. (This is also inferred in the SCOTUS video I linked to)
The "child in the womb is only where it is because of the risks the woman and her partner assumed, and in doing so, their consent for the outcome of their assumed risk is implied. The child they created is entitled to the equal protection of law, and it then takes an even greater (atypical) threat to the woman's life, for an abortion as an act of self-defense to be justified.
In the case of a rape / criminally induced pregnancy, there was no assumption of risks by the woman, no "implied consent" for the pregnancy that has been forced onto her in a criminal act.
The child she is pregnant with is still just as much a child / human being. . . but they are a real threat to the woman's life/health and well-being that she in no way invited, assumed the risks for, or even implied consent for it being there.
She does not surrender her right to defend herself against that threat when she becomes a victim of rape.
All this being said, I think there is a reasonable expectation for the rape victim/woman to cooperate with authorities to (when justified) have the abortion if she chooses to do so, as early as possible in the pregnancy.
Because her failure to do so would look more and more like "implied consent."
I challenge anyone else to give you a more thorough answer than this. I would like to read it.