Before, Epona was the horse of Link and of Ilia. all two had the responsibility to be occupied of her. But when Link had decided to leave the village with Epona, the villagers of Ordon had decided to buy another horse to direct the herd of goat.
Thus, they obtained this new white mare, Crystal, offered by the royal family in person in thanks of rendered service. And of course on behalf of Prince Zora, who granted to Ilia, the property right and of whole responsibility.
Now, It's Ilia who replace Link, for helping Fado to occupy itself of goats and to return them in the barn the evening.