It might be her child biologically, but I know for me I could never love a child of mine conceived in such a manner. Even with adoption there is always the fear that the child will try to find you, causing the pain to resurface years later. And what about the pregnancy itself? Being pregnant is a very public situation, while rape is something most women don't want to advertise to the world if it happens to them. Say you are married at the time of the rape. How do explain what happened to the baby without mentioning the rape? That's if you give up the baby, which would be a must, since no man wants to raise another man's child, especially if the child will clearly look different than the couple's other children.
O.K., so we agree on biology then - that's a start. Can you help me convince some others above? Good thing for us humans that God the Father does not say "I could never love you id you killed my Son." As for "no man wants to raise another man's child, especially if the child will clearly look different than the couple's other children" Joseph did not "want" to, but he did. Sometimes, this may come as a shock to you, humans are capable of the selfless act.
How lovely.