I don't think it was the rape that sent her crazy, it was the abandonment. She could have lived in her real world and been happy in it, if only Covenant were still with her. It was the lack of him that she couldn't live with.in her delusional world - where she was Covenant's queen and mother of his love-child - she was happy.
I'm not saying the rape wasn't distressing to her, it obviously was. But if Covenant had taken her along with him when he left Mithil Stonedown, she would have stayed sane.
From Covenant's viewpoint at the time, taking her along would have been admitting the Land was real. You can't have responsibility to a delusion.