There is nothing additional or special a woman needs to prepare. A woman has the same requirements as the man, to not orgasm, to not waste sexual energy. The couple obviously must respect her menstrual cycle and not practice when she is menstruating.
But in terms of preparing, I am not aware of any necessary period of time, like days or weeks, that a couple needs to stop fornicating before they can begin sexual alchemy. Sexual energy replenishes on a 24 hour cycle, so any new day is a day that the couple can begin practicing sexual alchemy. Of course, it is a serious commitment and should not be taken lightly.