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.
That's a big issue, but another is that teachers in a Catholic school should believe the Catholic Faith and accept Catholic moral teaching. This doesn't mean never sinning ... I myself holler, "Bleep bleep bleep FREEEEEEP!" more often than anyone should, and I'm excessively fond of wine ... but it doest mean correctly identifying sin, and that includes fornication and contraception.
Independent of all other factors, the presence in a Catholic school of a teacher who is pregnant outside marriage creates a climate of "Don't judge her choices!!! At least she didn't have an abortion !!!" We already have plenty of "Don't judge," taking precedence over accurately teaching Catholic Faith and morals, because of the family situations of students both Catholic and non-Catholic.