If I can add a suggestion... do different songs each day. This forces her to read the music and does not give her a chance to memorize. Just work on sight reading. Give her a few new songs each day and give her only one or two chances to play each song. You can pick up exercise books of varying levels and just blast through them. A lot have rhythm/clapping/other exercises to mix in as well. You can make a challenge out of how many new songs she can play each day or how slow/fast she can play each or play the right notes but make up her own rhythms to see how different she can make the song sound. You could also pick up a pad of staff paper and have her compose her own song and write it out.
Her teacher is obviously aware that she memorizes. Maybe ask her about adding in sight reading exercises next year. I taught piano through university and I had a few kids who were memorizers. We would spend time sight reading each lesson.
My daughter is probably the 'worst' memorizer out there. But, as she often reminds me, she has her own piano teacher. I have been instructed to stay completely out of it (by both of them). I can't even be around when she practices because we butt heads too much. I leave it to the teacher and dad and DD. If they want help, they ask. I would love to sit down with her and work on her sight reading, but that would never fly in this house.
Good luck!
