It was a huge shock. I've never had hair that short in my life! I think the rest of the cast and crew were mourning my haircut more than I was! But after a while, I felt liberated, I learned to embrace it.
For me everything in the film was gradually building, becoming more emotional, so it helped. At the end of it all I was emotionally drained. At that point I took Rose's view, that this has to happen, there's nothing I can do about it.
Because I was able to submerge myself into the character, I didn't have to go back and forth. You don't have to work hard to bring emotions. It all just comes naturally, you're there living it.