For the sake of your MC, let her forgive him and move on. You can decide later if they want to rebuild their relationship. If she finds out he was brainwashed after he dies, for example, she's going to have to live with guilt on top of all her other feelings.
But from IRL, forgiveness is just as much for you as it is for the person who hurt you. Not forgiving is like the adage about you drinking poison and expecting the other person to die.l
Like @GoldenHoneydew said, the biggest thing is what type of person the character is? If she can see the bigger picture and understand that her dad is a victim too, forgiveness is a logical place for the story to go.