Epona IS the Horse Goddess of Travel.Epona is one of the few characters to appear in more than one place at a time. In addition, her name does come from the actual Horse Goddess. She's also the only other character to appear in Mammon's World as is. Shannon simply can because she was created by Mammon.
Epona created the Wings.As mentioned above, if she does have the ability to travel anywhere, making Wings to get to those specific places wouldn't be difficult for a Goddess at all. Alternatively, she used certain monsters to create the wings.