The phrase 'toughen her' is correct and usable in written English.
It can be used to describe someone who is trying to become tougher or to put some extra effort into their work. For example, "Jenna wanted to make sure she could handle the pressure of college, so she began to toughen her by regularly lifting weights and practicing meditation."
I wanted to toughen her up, and give her a modern sensibility".
Although Jane doesn't have to make quite such a sacrifice, her suffering will surely toughen her for the next adventure.
Hazel is a straight shooter, pragmatic but principled, and her main function is to deal with an ethical dilemma that will toughen her up for future assignments.
Yet Mrs Gandhi conspicuously spurned a chance to toughen her support for the deal at a Congress shindig on November 17th.
Having chosen Sabrina once the girls hit puberty, Day worked to toughen her up by dripping sealing wax on her skin, standing her up to her neck in a lake (she couldn't swim) and shooting bullets at her skirts.The whole experiment failed.
But nothing can prepare you for waking up in the middle of the night, terrified that your child is going to be eaten alive by the world, she is too sweet and guileless for what lies beyond the nest of college and camp, you haven't done enough to toughen her, she's just not ready.
The experience also toughened her.
Burdette said a string of victories in Belgium had toughened her game and built her stamina.
Facing the anger of Jewish voters in recent months, she has since toughened her stance toward the Palestinians.
Mrs. Thatcher always reveled in a good fight, saying her opponents' vituperation only toughened her conviction that she was right in taking them on.
Years of challenging the regime had toughened her, and witnessing so much violence only made her determined to do her job as a journalist.
