I don't know about how the situation happened. But is it possible she could have misunderstood she was witnessing a guy forcing you?

My gf's and I had this promiscuous stage 'picking up guys' and fooling around with them, young teens, in the same room or the beach, etc... I'm imagining there could have been some misunderstanding in some way like that?

But if it was crystal clear to her what was happening, why would a friend just stand by and do nothing? Why would you blame yourself?

I had a date rape incident and I do blame myself so I never said a word about it when it happened. I stupidly went out with him in the first place, consented to go to his house, freely took a hit or two of a joint, vaguely remember (not consenting) but not even saying 'no'. I do believe he drugged me at dinner and that is why it happened, but you can see how the truth is foggy so taking self blame is understandable.