Mother of All is a portrayal of the Fear of Disorientation used predominantly in Tea Time with the Traitor.
While it appears that the Mother of All fulfills a similar role to the Empty City, a recent post on the blog makes comment that the Mother of All may play a role in the genesis, or renewal, of Fears.
As such, she is considered a primordial Fear, alongside the Father of All, not one with its own agency.