I do know I wouldn't leave it to emotional irrationality like asking if I'd do the same if she was "1 week" or "5 weeks" pregnant - that's as irrational as me asking you why you support abortion at 8 months.
I also know that since Roe v Wade, medical science has increased the odds of viability for a fetus outside the womb, narrowing the window in many peoples' minds about when an abortion is strictly a woman's choice. Many doctors who support abortion rights believe that after a shorter period of time there must be a medical reason to abort, not just a choice. It's why abortion as an issue is actively under discussion in the US.
While this is not an abortion issue, it is an issue of "human rights" and what should or could be done to save the life of the weakest among us. When there are two competing interests, one should always err on the side of least harm. In this case, there is no personal harm to the woman who as all have agreed is dead - the only personal harm from choice is to the fetus.