I just re-watched a segment of 2×21 “An Apple Red as Blood” and HE is right. Snow definitely has a sword in that episode as her weapon of choice. So, at some point prior to Prince Charming being taken captive, Snow learned how to use a sword. Maybe she learned to sword-fight as the only child and heir to King Leopold’s kingdom, especially since she became a daddy’s girl after her mother’s death. While perhaps unorthodox for a princess to learn fighting skills, as a crown princess, Leopold might have given his daughter extra “male” training should she ever need to defend herself and her kingdom.
It’s also possible that RH taught her to use more than just a bow and arrow. He might be known for being a fantastic shot, but he was also a great swordsman. Even in the Disney cartoon, Fox RH used a sword. He just an all around weapons expert. So we could adjust our timeline to say that RH taught Snow how to shoot and the basics of sword fighting between 5-4 years BC.