If you studied to become a teacher for half a decade, love your job, see the impact on kids who need you, and essentially work at a non-profit, there's very little recourse but leave teaching behind entirely and do something else in the private sector.
You can cut corners and stick to contracted hours but your classes will suck, your kids will know you don't care and won't care either. Both your job becomes boring, soulless, without impact or connection as the relationship with your students goes down the drain. You'll burn out for different reasons.
I'm exaggerating some points slightly but that's the gist of it.
Netherlands btw.
Is that fair? No, but it's the moral calculus regardless. And it's at least one reason why teachers are, indeed, "underpaid".
Why does she accept this? You get a salary, you have hours to do shit then go home and forget about work. You need to prepare things? Do it at school during work hours. Stop gifting unpaid time to a corporation which does not care.