Some additional memory sharpening techniques.

Make Good Hand Position

Most students remember what his hands look like while playing and keys off that. "Right hand goes up high here; left hand doesn't move" and so on.Using such method, some students find that memorizing hands separately is helpful, but most prefer to memorize hands together, as that is how the music will be performed. Hands-together has the added benefit of simultaneously memorizing which hand has to get out of the way for the other at which point, which notes might be taken by the other hand, and other "logistical" concerns.Like brute force, hand position is a dangerous memory method. I call it "finger memory." If the fingers slip, memory is gone. These two types of memory should supplement other types of memory, not be the primary element. 

Memorize While Learning

Some students prefer to memorize the piece as they learn it, rather than memorize after the notes are under the hands, as noted above.
The piece is broken into small parts (a measure, a phrase, or a half-phrase is a good starting point), and each is played slowly until the notes are mastered. Slowly!
Then memory work begins by playing as much as possible until memory fails. The student looks back at the music and again plays slowly, giving careful attention to the place where her memory failed her. 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. (Example: as soon as this B-flat is played, the Left hand  thumb must tuck under and rest on G so it is already there, rather than tucking the thumb in the same movement as playing the G.)
The next section is learned in like fashion, but now the student -also- focuses on the transition (the composer's mechanism) from the first segment to the second.
Because this is a fragmented method of learning the music, all fingering should be written in the score before the note learning begins so it is never in doubt. This also helps the does the student not to "fake it" or to use a variety of fingerings.