Hi, I'd like to help you with your question.
In your discussions with your step daughter, have you brought up what the Bio mom said to her about you and your husband? If not, that would be a good starting point. Since this problem was created by Bio mom, then it needs to be addressed by your husband and you. I would not say anything against Bio mom. Have your husband keep his words and tone neutral, but let his daughter know that there may have been some misconceptions about how you and her father feel about her. Then have your husband let her know you both love her and would like to have a great relationship with her.
Your husband needs to be the leader in these discussions with your step daughter. Since the Bio mom convinced the daughter that it was her father who is more interested in his new family than in her, then it is up to her father to personally dispute this and let his daughter know he cares. She needs to hear it from him and no one else.
You can also ask her what prevents her from being close to you and her father. She may have some unresolved feelings about the family breakup she needs to work out with her father, or she may be confused, sad or hurt. Many children do not have a chance to express how they feel about divorce and remarriages because much of the focus is on the adults and not the kids.
If you feel that your relationship is too fragile or that your step daughter's feelings are overwhelming, seek out a therapist to act as a neutral party and help all of you learn to understand each other and communicate better. You can find a therapist through your family doctor or if you attend church, your pastor could help. Also, you can search on line at http://www.findatherapist.com/.
Here are some books that may help you get started. One is called Stepmothers and Stepdaughters: Relationships of Chance, Friendships for a Lifetime by Karen L. Annarino and Jean M. Blomquist. Another is Divorce Poison New and Updated Edition: How to Protect Your Family from Bad-mouthing and Brainwashing by Richard Ades Warshak. You can find these on Amazon.com or your local library may have them available.
I hope this has helped you,