Sometimes it helps to consider possibilities "behind the scenes." I have been in a situation that--while quite unlike this in specifics--caused me to wonder about this situation. When people in an administration of any kind don't get along, cliques form and each looks for opportunities to take the other to task. By getting pregnant as a teacher in a Catholic school, this woman opened the door for her "enemies" there. If they were powerful administrators--or those who could influence those with the power to hire and fire--then she might have been the victim of their opportunity to be rid of a rival. I've been in this situation myself (just not as a pregnant teacher in a Catholic school, obviously).

What I'm saying is: the actual motive for firing her might be something that really has nothing to do with her being pregnant out of wedlock in a Catholic school. It could very well be nasty politics, as usual.