I think you can make this really positive, qpfrk.
You can say that a long time ago, you were married to a different man (or not, whichever is the case) and he was a mistake. He was not a good and responsible man, and he didn't stay around with his family. THEN, you met your Mr. Right and he loved you and your daughter so much that he wanted to be part of your lives forever, so you got married and he is your loving daddy. And now, he loves you so much we want to make it completely legal so he is going to officially adopt you and make you not only his daughter in his heart, but his daughter in the eyes of the law also.
Just be matter of fact, don't mention much about the man before, and make a big deal out of the fact that your husband chose to be her father and really loves and wants her.
I dont want her to feel hurt...............we both love her very much.
The Biological father has never wanted anything to ever do with her..........so she doesnt even know anything aout him.
Is she in contact with her bio dad ? I think you tell her the truth why would you be scared to tell her ?If she has no contact with her bio dad adoption may be a good thing, Tell her th truth ,as it is .