I adopted an older female Scarlet about a year ago. I am her third home. The first was a man, and the story goes that she "turned on him" after seven years and bit him agressively any chance she had. This guy had hand fed her from a chick and didn't abuse her. The second home completely ignored her, giving her cheap discount store seed only, and no toys or interaction. This bird literally had dust on her, and cobwebs in her cage when I went to see her. Dirty water, rusty cage, one perch....broke my heart. She really doesn't like men, but she will take treats through the cage from my husband and son-in-law. It has taken a year, but she will step up for me and let me carry her from cage to play stand.
If your gf is content to start slowly, I think she can get to a point where they can have a relationship. Just be VERY careful to have gf at a safe distance when you have the bird out of the cage. Don't expect too much too soon. Allow the bird to settle in, get to know your household routine, and she will be fine. She may never want gf to handle her...mine won't let DH handle her. He is fine with that...he still enjoys her company.
My scarlet is an absolute joy. She is such a character, and we absolutely love her! Good luck! That is a beautiful bird, and I know you would give her a great life!
Sierra