I agree with doing the plates in different colors, just vary the shades. If you can find a print that has most of the colors, that could be used as the centers to tie them together. Once they are done, you could lay out the plates so the colors make an additional pattern (like diagonal rows of tan, yellow, orange, chocolate, then teal) or just lay them on the floor randomly until you feel happy with the look. The most important thing is that you are making the quilt for her and it is made with love and joy - everything else is just details!