Oh that's very weird. The fight isn't supposed to be hard. The real challenge is keeping the sheep alive.
What level are you at? If you explored a bit, got some new equipment along the way (looting or buying) and is using each character's skills well, the fight should be pretty easy.
Jeanne can buff the team's defense, and Mao can do a ton of damage if you buff him with a fire rag or Jeanne's dark buff. The ogre is weak to elemental damage too so Lianna is great at the fight, but blinding it might be even better so it misses its attacks more often.
I hope that helps!
