It's imposable for ladies to fart whether awake or asleep,
the scientific reason for this is simple,
the female of the species cannot keep their mouth's shut for a long enough time period to allow the required amount of pressure to build up.
I had a friend who when camping with his two (so called) friends had a piece of poo wiped on his top lip. When he woke up in the morning, sporting a new brown moustache, he couldn't work out where the smell was coming from.