Depth perception is the process by which we perceive the world in three dimensions. It is an important component of our vision. If there is any defect in vision, it is important to see the eye doctor
(known as an ophthalmologist). This is even more important in growing children, as their brains are developing the visual pathways. If not corrected early, these will develop incorrectly. I strongly encourage you to take your daughter to an ophthalmologist.
We perceive the world in three dimensions. Our eyes use two general categories for seeing the world. The first are different cues used by the eye--known as monocular. These techniques like relative size and parallax refer to the way that one eye can "guess" whats closer and whats further away. Any problem with an eye can disrupt this.
The other way we perceive three dimensions is the way our eyes work together. These are known as binocular cues. Our two eyes see the world from slightly different points--so by integrating the two separate data points we can figure out where things are.
A failed depth perception test means that your daughter had problems knowing where things are in all three dimensions. The screening tests done by schools are not good enough to pinpoint why. We worry
if the binocular cues are a problem--this can be because of misalignment of the eyes--like ambylopia (lazy eye). This can be corrected is seen early.
I would strongly encourage seeing an ophthalmologist.