In May of 2003, Traditional Quiltworks Magazine offered an article to it's readers about the Quilt Code of the Civil War. In it, it explains how traditional quiltblocks were used to relay messages to slaves trying to escape from the South to Northern Freedom. The Sunbonnet Sue block is mentioned explaining that the block used must have been what we call Colonial Girl, Umbrella Girl or Southern Bell patterns. This issue is controversial, but if it is true, would of course mean that the pattern has been in exsistence since the 1860s. Visit this site to read more on this subject. It is very intriging and the site has links to many more sites of interest.
Southern Belle embroidery was popular from 1920 until 1950s. Here is an example of stamped embroidery pattern typical of the time.
Below are photos of typical patterns used during this time.
The second one is a pattern that I have never seen--A SBS Profile--it was purchased in Canada.