Look at the question the OP asks. He says 'am I wrong to feel aggrieved about this?'.
I don't think there is a right or wrong answer in this case as plainly put OP, no-one can tell you how to feel on the matter.
I don't think your partner did or said anything 'wrong' as it wasn't illegal or immoral to answer a basic question at a high school piss-up! It make might make you feel embarrassed but if you look at why YOU feel embarrassed I think there lies your answer.
I think a lot of people can openly discuss sex in public and feel no shame. I can discuss sex in public and feel no shame in it. It's when it becomes personal I draw a line. For instance if I was discussing dp in public and what he does, how he does it....I think I would feel 'bad' for him....like he deserves more 'respect' from me than me airing to everybody what his performance and technique is like. Because I don't view as a sexual plaything to be analysed by all and sundry. So I have qualms about certain aspects of sexual discussion in public.....but not ALL aspects of them. I can easily crack sex-related jokes and that doesn't bother me and I can have a bit of a smut-mouth when I choose too.
As I said earlier I think some things should remain private between a couple and other things, you should pay no mind to them. OP, look at why this really embarrasses you then weigh up for yourself whether you think you are 'wrong to feel aggrieved'. Your dp did nothing wrong in the grand scheme of things and I think if it was said in jest at a drunken do (would she say this kind of thing normally?) then you would probably do well to let it slide.
Maybe some people's life-maps are easier to navigate than others. Maybe your life was more straight-forward in terms of your love life. You might have found it easier to go from A to B with a partner. On the other hand maybe your parters life-map wasn't so clear so she navigated her way thru it on her own terms till she found the perfect partner. But at least you know she left no stone unturned when looking for you! 
As for the people in your home town... who cares what they think> It's how you two feel about each other that matters. And you deserve to feel safe in the knowledge and at least a tad bit smug that after her conquests she CHOSE YOU to spend her life with. I think that in itself speaks volumes.
Don't give her or yourself a hard time over this. She could have done any number of things which were much worse. Good luck