To find Ana's height above the water at the time of diving, we need to evaluate the function \( h(x) \) at \( x = 0 \), since \( x \) represents the time in seconds after diving.
The height function is given by:
\[ h(x) = -5(x+1)(x-3) \]
Substituting \( x = 0 \) into the function:
\[ h(0) = -5(0+1)(0-3) \] \[ h(0) = -5(1)(-3) \] \[ h(0) = -5 \times 1 \times -3 \] \[ h(0) = 15 \]
Therefore, the height of Ana above the water at the time of diving is
\[ \boxed{15} \text{ meters}. \]