Parry when the move would hit Kena, not before. The attack should already be hitting Kena when you parry. It's really more like a repel than a parry. Also stand still when doing it as Kena doesn't seamlessly transition from attacking to shielding (unless it's with auto canceled aerials but don't worry about that). Lastly as a general combat tip, don't use the lock on in this game. It's awkward since Kena doesn't strafe with it and it basically just makes you unable to use the right stick. Kena has really good tracking on her normal attacks so you really don't need it. If you need to follow your enemy hold L2 and use the right stick to followbthem manually. You can watch me do all these things in this Taro fight.