Forgiving The Rapist

My wife was date raped 10 years ago.
We have been together for 7 years, so it was 3 years before I met her.
She was at a bar with some friends, she met a guy.
She had just gone through a bad breakup and was in a bad spot.
She said he was cute and nice and she liked him.
She was drunk but not wasted, she invited him back to her apartment and he drugged her and raped her.
She told me about it before we got married, she has always blamed herself for it. She said it was her fault for inviting him back to her apartment. She believes it was her fault for even putting herself on that position in the first place. When she originally told me about it, it hurt me to hear it. Just recently she made reference to her past again and the date rape topic came up again. This time she opened up more about it and I asked her for details about it. I know I should not have, I should not have made her relive it. It is causing me much more pain and mental anguish this time around. I know it is not about me, it happened to her. She lived it, she experienced it. She still says it was her fault for drinking and inviting a man she just met back to her apartment. I have told her that there is no excuse for rape. She never gave consent, which means it was rape. He raped her vaginally and analy. She didn’t realize she had been drugged until a couple years after it happened. She always considered it a “one night stand”
She didn’t tell anyone and only told me.
I feel like it’s my fault, like I should have saved her.
If only I had met her 3 years sooner, I could have prevented it.
I keep asking myself, “why did this happen to her?”
We have been married 6 years and have 2 kids together.
I love her very much and I feel guilty that someone hurt her like that.
I am in therapy for depression and have discussed it with my therapist.
He said I have to “forgive” the man that raped her.
I don’t understand that.
How can that help?
My wife said she has moved past it and just wants to forget it.
She said she is grateful she wasn’t killed that night.
She did not get infected with any STD’s
She did not get pregnant.
She said she really doesn’t even remember it, it is all very hazy and she only remembers flashes of what happened.
Still it makes me feel terrible for her.
We have a good sex life and it does not cause her any issues in the bedroom.
I just wish I could have prevented it.