Don't let her cuteness fool you, Kanna! Before she could do anything to you, Headbutt her away from you. If you can't move, fire a Leech Seed down towards her head. Once you're away from her, use Double Team to evade any attack thrown to you. If the attack are too fast, a Flash should leave the Cleffa dazed. Finally, give that Cleffa Bullet Seed. Or if the winds get in the way, use Confusion!

Headbutt/Leech Seed~Double Team/Flash~Bullet Seed/Confusion

P/S: The reffing does look pretty.