As a CP social worker, I would advise your friend to contact her local social service department before, or when she becomes pregnant.
In my authority, assessments are done and we take into consideration if the offender has completed any treatment work, the outcome of that, and also we ask that the offender engages in a comprehensive sexual risk assessment and completes any recommendations from this. There are many factors to consider.
For example, it may be that the offender is considered a risk to pubescent females, but poses a low level of risk to males 0-16. Or it could be that they pose a risk to pre pubescent males, with no cross overs into other areas. It's a complex area.
I would always recommend supervised contact between the offender and children, with the offender residing away from the family home. Assessment of the mother would be needed to ascertain if she is able to identify the potential risks and act in a manner to safeguard her child.
Supervised contact may be the best your friend could hope for though, OP.
One of the rules of the sex offender register is that the offender cannot reside with, or have contact with, any child under 16, unless previously agreed. Such as through social service agreement.
It will be a long process for your friend to go through. Ultimately, she may he asked to make a choice between her child and her relationship.