Has she ever had any formal psychological counseling or processing testing at school?
What is her relationship like with her dad?
Your daughter has several issues going on here and I truly believe that further evaluations should be sought. First of all, your daughter may have suppressed negative feelings toward her dad but she brings them out on you. She may not truthfully appreciate the fact that you have a fiance because he is not her dad. She may really be suffering deep down inside with the fact that she may soon have a new "dad" in her life. To ease her frustrations and to ease your worries, I would seek family counseling or individual counseling from a family therapist or a psychologist where all of the feelings and concerns can be addressed on a continuous basis. Secondly, I would ask the school and/or pediatrician to evaluate your daughter further for ADHD or ADD. There should have been a follow up regarding that issue.