What confused me a little about that sentence is the verb منع, in particular the use of من in this case. Couldn't the same sentence have been written:
منعَ ظهورَها التعذّرُ, where ظهور becomes the مفعول of التعذر without using من? Because the way I understand the sentence is that التعذر has prevented the appearance of فتحة or ضمة or كسرة, so it seemed strange to me to have to use من in this case. I understand using من if I want to say something like:
منع الأب ابنه من الخروج من البيت
The father prevented or prohibited his son from leaving the house, but then I think I could also possibly say:
منع ابنه الخروج without من. I don't know.