Alex seems to like my quilting suggestion, however, nothing is final until it's final, so don't be surprised if she changes her mind - or takes one of your suggestions.
In the meantime, she asked me to share HOW to mark the "Raindrops" pattern I drafted for her. The three images shown above will show you how.
1. First, draw several "targets" that do not overlap. These can be drawn with a compass, or by using various round items that will nest into each other. I used to have a concentric circle template so I know those are out there too. Make the "targets" various sizes.
2. After you have as many FULL rings, then start doing them again, but where they overlap - just don't draw the lines. This will create the effect of drops that hit the water earlier so they are being washed away by the full versions.
3. Finally, fill in the gaps, again, not overlapping any of the lines. I think it is a pretty cool option.
As far as the size of these rings, it will really depend on the size of your quilt. However, I think the largest of all the circles would be about 7-9 inches - could be smaller. I tend to like the space to grow slightly as the rings grow out from the center, but that's only my personal preference. They could be evenly spaced.
I suggested that Alex use a thread that really blends, rather than stands out, because the quilt is somewhat light and the shadows and highlights created from these rings would really be the star of the show.