I had a similar awakening only in my case it was my girlfriend being spanked by her dad. Like you I didn’t witness it as I was sent home by her dad, but I did recreate it in my head most nights.
Most of my attempts to find out more about it were batted away by her who no doubt suspected I was enjoying the image far too much!
I do remember talking to her the next day and her looking like she might cry and saying something under her breath about how much she hates him!