why are you making assumptions about fictional women?
It was neither a fictional woman nor an assumption. It was a category of scenario, that category may never happen, it may happen often, I was showing that certain categories would leave to your application of your rule causing counter intuitive consequences. I am not saying that those scenarios happen, are you saying you are ok with if such a scenario were to happen then abortion would be made illegal to defend the life of the fetus?
if this pregnant person is indeed aborting this fetus for purely arbitrary reasons – not because she would be in danger – then, of course she is doing right by her not to be born child by not giving them both miserable lives
So if we could garuntee the baby not to have a miserable life, for example some wonderful family is willing to adopt the baby, then by this logic the abortion should be legally stopped. Doring so would uphold the two criteria you set: self-defense principle for the fetus and not having a miserable life for the fetus.