Although his approach was friendly enough, her response seems rather negative.
The first day of life for a baby is a never-ending assault of sensory stimulus. The physiological and behavioral adaptations that come in rapid succession when presented with the (new) external environment must be exhausting. The expression on this face shows evidence of this reality for newborns. The added stresses of a free range environment only accelerate the need for a foal to interpret and master volumes of new abilities in a very short amount of time.