The characters were not created by the Empress herself, but were suggested by an official named Zong Qinke, the son of one of her cousins, in December, 689 AD.
Her subjects were forced to use them during her reign, but they fell into disuse immediately after her death, so they help to determine dates of printed materials.
Wu was China's only empress, and she exercised her power by introducing many reforms.
For instance, 圀 ('country', 'state') is used to write the name of daimyō Tokugawa Mitsukuni (徳川 光圀) in kanji.
Anecdotes about the reign of Empress Wu and the creation of these characters can be read in the Old Book of Tang.