Congrats on sticking to your guns. My DH and I were in the same situation - we are your age and we were living at home until marriage, not having s*e*x until marriage, etc, so I get your dilemma. Sorry you're getting all this flack!
She could be the type of person who feels sorry for your 'old-fashioned-ness' and is trying to convert you to a 'freer' and 'better' (to her) way of life. Of course she is trodding all over your beliefs as she does so.
Next time it comes up, I wouldn't bean dip anymore. I'd be straight up: "I know I've shared a lot with you in the past, but our conversations have become too personal and are making me uncomfortable. I'm not interested in discussing this any further. I know you'll understand!" (Said cheerily.
And the next time it comes up, cut her off in a similar fashion (politely): "Oh, remember, I want to keep our conversation appropriate and work-related! Anyway..." then comes ye olde bean dip.
Maybe it'll work... You definitely want to stop it now, though, because it won't end after you get married. She'll just move on to talking about your married s*e*x life and how her suggestions can improve it! Yikes!
(BTW, loved your post title. Made me giggle.)