Well said, Ember. There seems to be something missing here. I'd definitely confirm her thoughts and don't get caught up in the apparently unbelievable offer she has made.
"Just having sex" may have implications that may only surface after the fact. Then it's too late to take it back. Even though she is suggesting this and isn't saying she wants the same freedom, try putting yourself in her shoes and imagine if she "just had sex".
Communicate very openly.