Forgiveness, at the Human level, is often a cathartic for the person doing the forgiving. Better to forgive and get on with your life than allow the bile of hate to eat at your soul. King David aside - if she were to hunt them down and kill them, God may or may not bless her, but she would pay a worse legal penalty than them. Kind of funny how so many who have probably never actually done any serious retribution/vengeance are so quick to exhort others to it. They also use the Bible to justify non-Christian thoughts/actions.
remember the priest who ran a spear into the couple as Moses watched? A man was bringing a foreign woman into his tent and the priest ran them through and God said he was the only person who did rightly. Interesting story. At His trial, Jesus was beaten on the cheek and He didn’t turn the other one so obviously it is figurative I can go on and on