* She wore a long white dress, a canvas of innocence against the backdrop of the bustling city. (Metaphor comparing the dress to a canvas)
* The long white dress flowed around her like a gentle waterfall, whispering secrets of a bygone era. (Simile comparing the dress to a waterfall)
* She was a vision in white, the long dress draping her like a cloud, ethereal and otherworldly. (Metaphor comparing the dress to a cloud)
* The long white dress, a beacon of purity, illuminated the room with its gentle grace. (Metaphor comparing the dress to a beacon)
The best option depends on the specific tone and imagery you want to evoke.