Her expectations were set by the students actions. You obviously haven't been in the average high school classroom lately. It's ridiculous. Kids get away with saying almost anything in class, and the teacher is near powerless to stop them. All it takes are a few to start the disruption and a few more to join in and then there is no more learning happening. Like someone else said, what can the teacher do to stop them? Kick them out, so they go sit in ISS, then come back the next day and disrupt even more?
And your view of your mother's work is extremely childish. "My mom changes kid's lives, she can make them learn no matter what the problem!" The students enjoy disrupting class because others think it's funny.
I'm not some white knight for teachers, they have a lot of faults, but give them some credit. Most kids in my generation are pieces of shit, mostly because of bad parenting. And the cycle will continue...