I admire your courage and persistence in dealing with this, and it does sound like it is time for a change. If I am reading your email correctly your husband fathered your stepdaughter while he was in a relationship with you, yes? This is important because she has been in the middle of your relationship right since the beginning. Whatever conflict was in your relationship back then she is connected to.
Yet you have done a terrific job of reaching out, extending yourself, and making the best of the situation. But this situation, and in particularly your stepdaughter, needs some outside help. Her anger, your husband’s reluctance, and your frustration are building. While it would be impossible for me to know for certain there is a good chance your stepdaughter is angry toward you because you are the woman her father married, instead of her mom.
Your insight about her needing counseling is very accurate. My guess is that she doesn’t fully understand her own feelings, which would not be unusual for a 12-year-old and it may not be safe for her to talk with you or her father about them if she did.
Your husband doesn’t understand your feelings and your stepdaughter mistreats you. You tiptoe around her, and there is no arrangement for her to be with her mother. You seem to be the only one in the family trying to work toward a resolution.
It is time for you to stop trying to fix your stepdaughter, your husband, and the situation and refocus on your needs. Right now you have a very difficult decision to make and the people closest to you are not helping. I would encourage you to seek some brief short-term counseling to help you sort through your options. Right now your husband and stepdaughter are not giving you any signs that they want or are willing to put any effort into change. This is a time you need to be thinking about your opportunities and your own future.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral