It's not about the baby. While tragic to lose a life what message to we send a girl that she is forced to carry Daddy's child/grandchild and then has to go through life knowing such an abomination exists that she helped (not of free will) create?
It's ugly and really just a no win situation but I (JMO) think that that there are some things society can't make people participate in.
Here's the bottom line. You do not have the right to kill any human being on earth ever, except for yourself. Even if you don't like the circumstances of their birth, you do not have the right to kill them. Period. If you or anyone has that right, then I have a right to kill people based on what I don't like. I think you see where we go from there.
Who decides what is an 'abomination' and what is not?