If its any comfort to you your dream was probably a product of the fact that you're thinking about the girl on the anniversary of her death. It's hard when someone cares about you dies, i too have lost many of my peers at a young age so i can understand your grief 3 years on, you never really forget a friend who's no-longer around and it does get easier as time goes on. I think the best thing to do is just go with any feelings that you have at the time and express them, dont keep them inside, even if theres no-one around to listen. Try not to think about what could have been and just remember fondly the experiences you had together and the time that you shared.