I'm not sure what you mean with this.
Would it be a correct translation to say "She speaks when she sleeps"?
What i meant was: there is a usual expression in English for when a person walks about while asleep - "She sleep walks", but there isn't one for talking while asleep. "Enquanto" means "while", that is "for some of the time she is asleep" but not all the time or every time." "Quando" means "when", possibly all the time. "Whenever" means all the time and every time. Whenever= "sempre que", but you need a Brazilian to tell you if these three expressions overlap as the English ones do.
why not dormindo? when using "while" (enquanto) it is implied so no need to use gerund?