It stimulates the part of the brain that helps to keep you awake without stimulating the entire CNS. what that means is you can stay awake but you don't get many of the side effects that are common with normal stimulants.

It shouldn't affect her ability to sleep, most people have found that they can even take naps, if they feel the need to, while on the medication.

Take it on an empty stomach and wait about a half hour before eating otherwise it doesn't seem to work as well.