Ok so after reading through your entire post and consulting with myself and my dragon allies, I know who you saw. The White Dragon, Tiamet, the Mother of Dragons. The fog/mist you are seeing around her is the Mists of Chaos and Time, the formative material of existence. I have worked with her for years and talk to her every single day and I have no doubt in my mind this was your subconscious trying to show you what may be a very important part of your path. She (Tiamet) states that you should consider seeking her out in the near future.