If she has a way to shred leaves, they make a good winter mulch over the garden. If possible, you want to add grass clippings too. The green stuff helps the brown stuff break down. She probably does not want to just rake leaves over the garden; they tend to turn into dense, soggy mats that do not break down and have to be removed in the spring. With the shredded matter, you can just move it aside to make a planting hole.