de son plein gré
Of her own free will would she have to give him her blood.
Elle devrait de son plein gré lui donner son sang.
— Nosferatu (1922)
Is she acting of her own free will?
Agit-elle de son plein gré ?
— Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train (2020)
I went there on my own free will.
J’y suis allé de mon plein gré.