@mootmar: Well, I don't know about that. Another reading would be: The timing of the waiter entering and him stoping coincidentally happen to be at the same time with her traumatic memories resurfacing. So whether or not him stopping was due to her reaction or the waiter entering is frankly not made very clear. Him scrunching up his face and being rather displeased by the waiter's entering, though, to me at least, suggests the later.
There's more to my discomfort though: I think that a sexual encounter that is to be described as consensual and healthy, no matter with whom, in what shape or form, requires both parties to be comfortable first and foremost. She clearly is not very comfortable with the situation. "I am scared" or "NO!" are NOT things someone purely enjoying sexual stimulation should be thinking. Not being able to clearly express this discomfort is part of the problem in that a lot of women (but also all kinds of otherwise oppressed people) are taught to not question or comment their treatment, let alone resist it - whether they like it or not. Granted, she does tell him to stop "down there" but seemingly can't go as far as just stopping that situation altogether. And making concessions like that - clearly being uncomfortable but still feeling as if one was obliged to let them continue whatever they are doing - is part of the problematic feeling of not being (fully) entitled to do so, to resist or stop them.
Edit: In this respect, I find it rather telling that she isn't looking him in the eyes when she's allowing him to continue...