Scene that got her suspended from teaching was horribly done.
She looks for the girl and can't find her. So she calls for her and another kid says she left with her father.
This comes as news to the teacher. She did not know that the girl left with her father.
The father that does not have custody and that the mother told her not to let the girl leave with.
Since we can assume that she would recognize the name of the man that came to take the girl (as the mom said she told her not to let him take the girl) this indicates that she did not even talk to the guy.
So some dude came into class, took a kid and left, and she did not even notice.
That had nothing to do with her face blindness and everything to do with her being the worst teacher on earth.
"What the f-ck is the internet?" -Jay, Jay & Silent Bob Strike Back