3 years of her attacking Kratos, and Kratos never fighting back.
Atreus going to visit her and talk to her.
When she came back as a valkyrie, atreus transformed to attack her but Kratos stopped him and said dont do it, shes our friend.
Told her he didnt never fought her cause wether she killed him or he killed her, it would be a lose lose for him.
and then in the trip to vanaheim, while she was a bird, it was the first chance since Baldurs death where they talked. Kratos told her of some of his past. After the fight, he apologized but never down played his death.
Now is that enough to forgive him? Maybe not. But the game did throw a bunch of stuff in there to make it more believable without adding abother 2 hours to run time.