"NO" implies a certain intonation of voice. You're prejudicing the question. If by "NO" you mean that the woman is shouting, or otherwise, firmly and seriously insisting "NO," and is overall expressing, in her body language, intonation of voice, words, etc., that she does not want to engage in sexual contact, then yes, "'no' means 'no.'" If she has just pushed your hand away, has a frown on her face, and has just said "NO" in her best Darth Vader impression, then you most certainly should stop what you are doing and respect her wishes.
That's not always the case.
Sometimes, that's not how she is saying "no." Sometimes, she says "no" in an intonation of voice, with body language, with behavior, and, in general, in a general communicative context that actually means: "Yes!"
That then is another issue.