Portman has spoken about the experience in a number of interviews, and how it fits into the larger narrative. She spoke to Charlie Rose when the film opened, talking about the entire film as a discussion about when violence is justified, and what makes someone a freedom fighter versus a terrorist. She spoke about Evey as moving from “someone who is too scared to speak her mind, her opinion, who loses her fear.” That scene has a lot to do with that.
She explained the character’s film situation in an interview with CBR as well, saying:
“I think it’s because she starts off as this passive character, which is like the ‘everyman,’ who’s just sort of like, ‘The government’s pretty horrible, but I’m just gonna try and keep my head down, go forward, go on with my life and let it work,’ and she gets swept up into this by accident, and then slowly learns to understand the political situation and that she has to become active. So, it’s a really exciting arc, someone getting their political consciousness.”
In the film, as opposed to the graphic novel the film is based on, Evey isn’t already in a desperate situation as a waif on the streets. She’s middle class and comfortable, and in a way, this dissolution of her vanity when her hair is shaved is the thing that takes away her fear. She’s lost an outward symbol of who she was, and now she is free to be someone new.