I'm sorry, but as a father of two teenage daughters, I have to play devils advocate here and ask you, what if your 13 y/o decided to keep the kid?
Keep as in raise it herself, or keep as in give up for adoption? I would be against the former and for the latter.
The child is your grandchild. And, you don't own either your daughter, her body, her life, or the body and life of your grandchild.
There is either a right to life that cannot be infringed or there is not.