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It sounds as though it may be a fungus. There are several it could be but, fortunately, they are all treated the same...with a fungicide. I personally like neem oil as it treats both fungus and any pests that may be hanging around on the plant. Here is more information on neem oil:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

The urine may have made the soil too acidic and salty, which will slowly kill the plant. Really, the best thing to do is to flood the area with the hose as you have done to help wash the urine out of the soil.

As for the plant, check the stems to see if they are still alive (https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm).

Seed grown camellias are seldom true to their parent but will still be suitable for growing. This article will help with propagating these plants: https://www.gardeningknowhow.com/ornamental/flowers/camellia/growing-camellias-how-to-propagate-camellias.htm

Generally, most shrubs can be pruned back by a third of their growth. Any more than this can damage the plant. Here is more information on pruning camellias: https://www.gardeningknowhow.com/ornamental/flowers/camellia/pruning-camellias-how-to-prune-a-camellia-plant.htm

Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/camellia/identifying-and-fixing-problems-with-camellias.htm

We would say they probably would not be getting enough water. It is very difficult to burn the leaves through daytime watering. You would have to have very intense sunlight and the damage would appear as spots and not whole leaves turning brown. Plants in containers, especially in high heat, should be watered twice a day (with good drainage), once in the morning and once in the evening for optimal water absorption. Most people water them only once a day and this is what results in damage to the plant.