I am trusting the word of the many women who experienced what they did at the time.
It was obviously not enough of a problem for them to reject her. But I mention it to counter your claim that her skill was in such demand that
of course they would not let her go, even if they found out she was pregnant. The timing of when they changed their mind is consistent with Warren’s story.
There is no evidence of the principal firing Warren due to pregnancy. (Outside of her late newfangled claims.)
As I said, it was not a “firing”. And her claims are not unusual.