Valerie is fought four times throughout the story.
Chapter 14: Time RevesalEdit
This battle is quite long due to the geography of the field. Elle and Glen are not available in this battle so be sure to level up your substitute healer for this purpose.
Valerie is very far at the back of the field and won't move at all until all enemies except the Fomoires are defeated. Luckily, all enemies here are weak against Light-based attack and if Inaluna reached level 35 she will learn Photon Axis which reduces the difficulty a lot. The Fomoires can cast Jungle Combo which may inflict slow but they may also use Palalyze then Heavy Tackle you, however the most dangerous is the Scyllas' Cold Kiss which may freeze you which allow them to easily kill you regarding your levels. Valerie on the other hand, favors powerful physical attack so either uses Heine's high defense or Dino's high evasion to couter this. Lunar Strike is unavoidable though.
If you fully deplete Valerie HP you will recieve Lunar Fur for your problem.
Chapter 21: Aura LapisEdit
Chapter 23: Time TrialEdit
Chapter 25: Life and DeathEdit
This is the final battle with Valerie and the hardest one of all. Since the panels are poisoned equip Rock Charm on all Landwalk Unit to negate this. Vim can also be used intead of Rock Charm and Skanda Garment is also helpful.
Valerie will first move toward party members. Her main target is neither Inaluna nor Arnogia but is instead Levi. Night Scream is nothing to be scary about, however Black Nebula can still deal devastating damage in large area. Her Flash Drive Lunar Strike's is still up to 3 panels. Valerie is still vulnerable to Fire and Light magical attack so Ignis Blaze and Photon Axis will work wonder. The Banshee may tries to heal her so be sure to remove it first. Also, beware of the Ghasts' Ultra Explosion as well.