The phrase "strain herself" is correct and usable in written English.
You could use it when referring to someone making an effort to do something difficult or to achieve a goal. Example: Mary worked hard to prepare for her presentation, straining herself to make sure everything was perfect.
The strain of forcing herself to take step after step to bring things to an end begins to exact its toll, because the predicament never ends.
But for the 22-year-old from west London this was not a pressure that stemmed from teachers and artistic directors telling her to lose weight, it was a strain she put on herself that eventually developed into an eating disorder.
Gill shows Victoria herself straining at the bonds, sometimes shockingly so.
She had always sung quietly, and in big rooms she found herself straining to belt out notes.
I've brought her a few violets and marigolds, picked from our garden, but when she strains to raise herself, lines of tension crease her forehead, as if she's struggling against two hands holding her shoulders down; after a while she gives up and falls back, exhausted.
"What did you wish for?" a middle-aged woman asked, straining to make herself heard above the noise of the crowd.
Where nature herself strains at her bonds: straining for release from the carbon blanket that presses against her too hotly, maddened by a thousand poison-filled wounds?
Former Alaska Gov. Sarah Palin, straining to inject herself into the 2012 Republican primary, accused Newt Gingrich's critics of imitating the former communist dictator of the Soviet Union, Joseph Stalin.
She waits until Jonas leaves for the day, so she can brace herself, heave, and strain in private.
Though Andy's staying was an inconvenience and a strain, too: my mother acquitted herself with exemplary generosity; she really did.
