In a stepparent adoption, the stepparent who wishes to adopt will have to file a petition to adopt, asking the court to allow him to adopt the child. You will have to file a consent to the adoption, as her parent. If your daughter is over 12, Colorado law requires that she indicates her consent to the adoption.
The rights of the other birth parent (in this case your daughter's biological father) also need to be terminated in order to make your daughter available for your husband to adopt. However, because your daughter was the result of a rape, this is complicated in this situation. If you don't know who her biological father is, you can explain the circumstances to the court, and the court may waive the requirement of termination. Generally, in order to explain not knowing who the father is, you must offer a valid explanation to the court. These circumstances are an adequate explanation for not knowing a father's identity, rather than explanations like "I was drunk and had a one-night stand."
If you do know who her father is, but don't want to reveal his identity, because of the situation, you could still provide an explanation to the court, but there is a good chance that you will have to provide the father with notice of the adoption so that he can consent (or dispute) the adoption. Even if the father disputes the adoption, as long as he has never had a relationship with your daughter in the last year, and has never paid any money to you on your daughter's behalf in the last year, then his rights will be terminated.
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Best wishes with the adoption!