She is one of the 4 Goddess Units that got released, a few weeks back.
Anu, Danu and Tartu are used to enhance your units by 3 levels. (Anu = Melee, Danu = Missile, Tartu = Magic) If you do it wrong and feed one of them to another Type of unit that does not correspond to its nature, the targeted unit that you want to enhance, gets upped by 1 level only. So make sure not to mess that up!
Epona, on the other hand, is only there to be sold off for 100,000 Luna. There is no other real purpose to her, other than feeding her to Leana and get 600 Points.