PF EXP Help.

[Nosta]

so I am running a online Pathfinder game with some close friends as we do this as a casual thing, cause we can't always meet up for are In person Sessions.

My question is the five level 4 characters will be facing a level 6 path of war human who uses mithiral current and has ok stats "She's holding back a lot"

Story wise she testing the party. Shes actually a level 18 character But she'll be acting like a level 6 character. it will be nonlethal damage but I still want to give and exp reward for beating her in this mock battle

how much should I give?

[Shark Uppercut]

The best course of action would probably be...
First, draw up her lvl18 stats. You don't need exact stuff, just general guidelines. 2-3 most damaging maneuvers, 1-2 favorite stances, HP, saves and AC. Now tuck those away.
Draw up stats for her, as a lvl6 character. Have exact, detailed stats. She'll probably have 50-70hp, only lvl3 maneuvers, save bonuses under +10, you get the idea. She won't have 100,000+ gold for magic items, as a lvl6 character should only have 16,000 gold total. That means probably a +1 or +2 weapon, a +2 Belt of Strength, weak stuff.

In the fight, do lethal damage, just like a normal monster. She's already holding back enough.
A lvl6 NPC is CR5, meaning 1,600 exp.

Once the "lvl6" character is defeated, she's lost her 50-70hp, make the fight stop. Remember, she still has a lvl18 character's amount of HP, so she's still at 2/3 health.
She tells them the test is complete. They get the experience, the story continues.

If they keep attacking her, start using her lvl18 stats, particularly saves, AC bonuses and Stance benefits. If they refuse to listen she'll use high level maneuvers to deal nonlethal damage and knock them out. Or use Veiled Moon maneuvers to teleport away.