Conclusion
I would never say that Sally's fantasy is a sick one, and I have no idea why she assumed that I did think it was sick. I feel, however, that Sally needs a great deal of help in order to come to terms with her own sexuality.
She is a girl who was witnessing orgies before she even had one experience, acting like a pro when she really knew nothing. She was also a romantic, waiting for the right man and the right moment.
Sally was quite upset with the way she lost her virginity, and that's where her whole fantasy stems from. In the fantasy, she is losing her virginity all over again. In fact, everything around her is white. This time, however, she is being forced to do it, not by sweet words or fear that someone might realize she's a virgin if she doesn't, but by sheet physical force. That saves her from feeling the guilt she most obviously felt when she first lost her virginity. It's going to take her some time before she can learn to enjoy sex with another person, but it's a definite necessity that she does learn to enjoy it.