When she thinks she can get beyond that breakdown point, she looks away and tries the section from memory. If not, she breaks the section into smaller units and focuses on those, isolating the exact point of breakdown and what her hands are doing or not doing. Backwards I learned technique this from a student. First he divides the piece into many little segments, some as short as a measure or two, depending on thematic material, key, or other common elements. This system has the added benefit of making the conclusion of the piece especially secure.
Some students are able to memorize away from the keyboard by looking at the score.
This requires an above-average familiarity with the notes and an excellent visual memory. They hear each note as it sounds and recall each finger, hand, and arm movement necessary to produce it. When memory becomes fuzzy, the student knows that is a place that will need her attention again. This is another memory check. Play the entire piece lento .