Epona is a very likable horse, but I don’t believe that she will be able to win in this battle. Nami has her Weather staff that can summon various elements and these would deal a lot of damage to Epona. Epona doesn’t really have a way to escape from Nami’s attacks and she will eventually be defeated. Nami is very athletic to she would be able to dodge any incoming charges from Epona. Nami wins.