Is it offensive for a non-muslim girl to wear a head scarf?
I don’t think there is any harm in it. Indeed, head scarf is not only Islam’s property. Even Mother Mary wears one in most depictions. Besides, the Qur’an says that it is recommended on the ground that it can give women protection (probably from men’s gaze). If you think it will give you the protection that it might offer, go ahead. The prominent movie critic and theorist, Judith Butler, says that, with regards to movies, women are objects to male gaze. Or, in other words, male gaze degrades a woman from a person to an “object.” Headscarf probably a way to resist this objectification and, as Eyad Zahra says, redirect men’s attention from the physical look of a woman to what the woman says or thinks or politically stands for. And if you see a Muslim men/women who are offended by that, you might want to kindly remind them about this.