Personally never had - what was the word again? - queefs, but made sure never to eat "farty" foods 24 hours before my yoga class...
Kegels logically would tone that area and help reduce airflow in and out, but you would probably have to do at least a 100/day for a few weeks to see any difference (which is worth it, in my opinion, especially as there are all kinds of added benefits).
And stretching on your back/legs in the air before the class if possible, to let them out.
Again,