There is a virus pathogen that affects blueberry leaves, and the resulting disease is called "blueberry scorch." However, it is possible for the leaves to develop similar symptoms from too much sun, and that condition is also called "blueberry scorch." I am having similar problems with some of our established blueberry shrubs, although it has not been too bad so far. Only a few leaves are affected on our shrubs. I know of no simple method to detect the virus, however, if the same symptoms appear next year, and if the flowers turn brown, before they have a chance to develop, then the virus is likely present, and the only solution is to get rid of the shrub, and start over. If your shrub is suffering from too much sunlight, the solution is to shade it somehow. Keeping it watered is necessary, but that will not prevent the leaves from turning brown, in my experience. The roots will continue to grow all summer, and into the fall. Chances are good that next season, you will not see this problem, because the shrub will have a more developed root system.

Shade the plant so direct sunlight isn't hitting the container itself. Given your location and temps you may wish to shade the entire plant during mid day.

Roots lose their ability to function properly beginning around 85F and over 90 even worse. In the low 100s the plant is dead.

This usually isn't a problem for plants grown in the ground, but it is for plants in containers as the containers don't insulate temps well at all.