User blog comment:Angel of death 77/Bethesda developers creating new content for skyrim/@comment-168.30.144.248-20120213160919/@comment-4058895-20120216092358

Lucien Lachance refers to Shadowmere as a she and his "old and dear friend", this means that the Shadowmere in skyrim is the same as the Shadowmere in Oblivion and since Shadowmere was a female in Oblivion its logical to assume that the gender is also the same. Our own wiki also states that Lucien calls Shadowmere a she but Astrid calls Shadowmere a he, this looks like the gender of Shadowmere is uncertain so we should assume that Shadowmere is female based upon the dialogue and references to Oblivion.