I think people often blurt out the truth when put on the spot - who knows what spirit the OP's wife divulged this information in? School reunions are famously psychologically weird affairs, full of people re-encountering teenage friends, former bullies, past selves, and there's a lot of remembered misery, showing off, and silliness. It's perfectly possible that, while the OP knows the information to be true, no one who heard his wife at the reunion believed her for a moment, especially if it was in the context of a silly drunken game, where everyone tells all kinds of lies.
I think she is entirely entitled to divulge personal information on her sexual past as she sees fit, and deal with the consequences, if any.
Also, could someone enlighten me on what the correct number of sexual partners for someone to have had before entering into a serious relationship and marriage at 33? Two? Five? Twenty? Fifty?
I ask because I got together with my partner in my late teens, and have been monogamous since, so I've had very few sexual partners - something which has attracted criticism from virtual strangers. And no, I didn't discuss my sexual past with my colleagues or at dinner parties, but once some people realised how long we had been a couple, there were acid little remarks about it being a shame, and inexperience, and committing too young etc.
Fortunately, I am an extremely forthright person, so they retired crushed, but would be interested to know what an acceptable number might be...