Okay, so Sibyl is just trying to mess with people's heads here. She cast Dancing Lights to summon, and I quote:
Four glowing spheres of light (which look like will-o’-wisps)
Figuring that they realize she is a spellcaster from what she has already done, she's faking that she summoned four will-o'-wisps and is essentially ordering them to kill the ghouls (who would stand no chance against such creatures).
In reality, she's sending dancing lights at them.
So here is a bluff check:
1d20+9=28
And because of the situation, an intimidate check might also be in order:
1d20 5=19
It may not be necessary, but I thought just in case.
I'm just trying to get them to run.
Now, another DC 17 save for the luminous ghoul...
Damage:
1d6=6