People who are unable to care for their child for any reason should be able to give them up for adoption or foster care, although I have to point out that the foster care system is deeply broken and abusive in many places, which makes this very complicated in practice.
But in any case, "in an ideal world" she would simply give the child up for adoption if she can't properly love the child due to the trauma of having discovered that fact about the husband. The child could remind her of him all the time so it's an unreasonable expectation.
A person who hasn't had any personal relation to the man would probably find it much easier to overlook this fact about the biological father. To the adoptive parent, it's just a poor kid whose dad came out to be a monster so his mother couldn't bear to raise the kid.
