Susan was just stepping out of one of the many fireplaces in the Atrium, she'd had an errand to run, when he saw the fire ball and stepped instinctively back into the shelter of the fireplace that was now silent. glancing the direction she saw a door close but little else as she waited for the initial debris to settle and could see the fire still burning.
Almost with out thinking she summoned the water from the fountain and sent it onto the fire. She heard a distinct sizzle, but knew it would not be enough. Fortunately the explosion from whatever started the magical fire had put holes in the roof and the smoke had a way to escape.
Casting jets of water was probably fruitless as most magical fires had to burn themselves out. And they could only do that through lack of fuel. She began to spray the wall nearest to her. people would just have to deal with a wet floor if all the wood work was soaked there would be nothing to burn.