One can see that kind of reasoning leading to a sort of moral blackmail: "Nobody is allowed to disapprove of or exact consequences for any sexual behavior ... because at least I didn't have an abortion." That's almost the default setting already for even the most irresponsible actions. "Don't judge me - I didn't have an abortion."
Yes, as I said, I’m a little hesitant about this—not arguing that the decision to fire her was wrong.
She committed a serious sin, and set a bad example for the children. It doesn’t really excuse her to point out that she could have doubled down and committed an even worse sin.
In the old days, before the Sexual Revolution, she would have been fired from a public school, let alone a Catholic school, because the first consideration was not to have teachers who set bad examples for the kids to imitate.