because you want to do sth rather than because sb has told or forced you to do it :
She left of her own free will.
because you want to do sth rather than because sb has told or forced you to do it :
She left of her own free will.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005