So it could be a few things

1. Very vivid sex dreams, I used to get them constantly.

2. She's so ashamed about it because of her upbringing that she's afraid you'll look at her differently - this I doubt because she should feel safe enough with you to know you wouldn't judge her

3. She's being a hypocrite and trying to control how/ when you orgasm. But won't give you the same respect.

4. She likes being able to cause you to think you're going crazy