Does this benefit the child?

First of all, you ARE her parent. Even though she is not your biological child, do you treat her, love her, and care for her as though she is your own? The bio-dad of my children has no contact with them. In fact, he's never laid eyes on our son, who will be 4 in December. He's not spoken to or attempted to speak to our daughter, who was 20 months old when we left, and is now 6. He did talk to her on the phone for about 4 months after I left him, but all communication ceased when I would listen in on their conversation, and heard him telling her things about me that were inappropriate. It was then in the best interest of my kids for him to no longer speak to them. The way I see it is this: my children's lives are not a revolving door for him to enter and exit at his convenience. It isn't healthy for them to go through that. So in regards to your step-daughter, my suggestion is you and your husband seek counseling for her, then ask the bio-mom what her plans are. Is she going to remain an active part of her daughter's life, communicating on a regular basis and physically visiting her, or is she going to abandon all responsibility? Luckily for me, my children's bio-dad is giving up his parental rights to my 2 kids so that my husband, who my children call Daddy, can adopt them at the end of the year. That is what my husband, both of my kids, and I want to happen. That sort of thing may not be what your family would want to do, but if bio-mom is going to continue a behavior that is destructive to her child, your step-daughter may, now or in the future, want this to happen so that she feels more secure in your family unit. Good luck to all of you. I hope that everything works out in the best interest of your step-daughter.