I understand your desire to have your daughter apologise but I'm not sure that having 30-40 minute standoffs until she says sorry is a good idea. It seems like it's just making her more and more upset rather than teaching her anything. Maybe it would be more productive to wait until later in the day and give her and both of you time to calm down before you discuss what happened and talk about how she was feeling and what you felt when she hits (if she's feeling able to express herself, that is, since you mention she finds it hard). The thought of someone forcing me to be held until I do something makes me feel uneasy, so it's probably a lot more overwhelming for a distressed 6-year-old.