There is no guarantee she will foal at night . . . .
very true... Chloe has had 5 foals (3 with previous owner and 2 with me) and the two she had with me was early afternoon (like 1-2 pm) and the other three was a mix of day/night.
I would just play with the camera settings and see what works best. Can you possible have a light on the outside of the stall instead of directly in it? It may cast enough light...just a thought.