This can only mean one thing- IT'S DESTINY!!! Actually, I don't know. I actually wrote a book about this sort of thing, except it was a girl that was madly in love with the guardian angel in her dreams.Maybe she's your future bride or a guardian angel God sent to keep you company in your dreams? (Sorry I'm weird -.-)
You know the truth buddy.. You can never ever dream about a person or a thing you havent seen till then... You have dreamt about the girl you have seen somewhere but failed to notice, but your subconsious mind took a note of it. Just find out who the girl was and say her, I love you. Marry her by walking in the aisle just like the film 'A walk to remember!!'.
Scientists have declared that every person in our dreams are real. We may not remember seeing that person, it could have even been a passing glance, but that person is thought to be real. As for her personality, I assume you have her those attributes. Hope this helped.