As far as Steiffgal can tell, this item does not appear in the Sortiment as a regular line item. After a little digging, she suspects that it was made especially to be one of the passengers on the company's mid to late 1920s-era pull toy novelties. Specifically, given the rabbit's size, color, era, and presentation, it is possible that she was produced to ride on the company's Galop-Fux novelty. This is pictured here on the left; this wheeled wonder was in production from 1926-1929. This image is from Pfeiffer's 1892-1943 Sortiment.
Galop-Fux consisted of a little grey running rabbit and a red brown fox that were mounted upon an elaborate metal wire chassis. Their cart had four red wooden wheels. When pulled along, passengers on a Galop toy shuffled back and forth in opposite tandem; the rotation of the front wheels was responsible for one animal's movement, while the rotation of the back wheels was responsible for the other one's movement. The running rabbit form would be perfect for this sort of effect.
It is interesting to note that there is precedence for Steiff making unique items for their 1920s-era pull toy novelties. Like this rabbit, these rarities did not appear in any other sizes or as stand-alones in the line at all. For example, the Galop featuring a Molly and black cat version included a c. 10 cm tall standing and unjointed black Tom cat. He is fabulous for sure - but does not make an appearance anywhere else in the catalog ever, as far as Steiffgal can tell.