I am not familiar with a blue leaf hydrangea. I assume you meant a blue flowering hydrangea, no? The leaves are always green.
Wilting on hydrangeas indicates that the leaves are loosing moisture faster than the roots can absorb water. It happens on windy days. It also occurs when the plant roots are in water for too long of time and develop a fungal infections that causes root rot. In a few cases, the leaf or the stem leading to the leaf is bent and the vascular system of the plant cannot send minerals, food and water to the leaves. Water falling to the plant or windy conditions could cause this.
It sounds like the plant needs to be transplanted to a location where the shrub will not be stressed out as it is now. Keep it well mulched, evenly moist and inspect it regularly for a month or so to see if things improve or not.
If the roots have been in standing water long enough to develop root rot, the plant may need to be replaced. Other than extracting a plant and inspecting the root system, I am not aware of any other way to check for this problem (if the damage is somewhat advanced, the affected roots may be smelly when you extract the plant and inspect the roots).