This dream, in particular, is all about you facing your fears of death. Your friend is helping you do this, indirectly. A room represents an aspect of your own self, and this was a bedroom, so it represents the room in which you attempt to reach higher awareness. A window symbolizes that you have the capability to see beyond your present awareness, and the light symbolizes knowledge, peace and truth. One has to face their fears first.
Darkness symbolizes the unknown, while light symbolizes knowledge and truth.
Even when we don't consciously understand our dreams, our subconscious mind picks up on it and works at deciphering it in the background. When a dream is very important for us to figure out, we will be nagged by it until we do. You do know don't you that I'm not really here. Remember that this was said to you by your friend, who represents an aspect of yourself. This is most likely the part of you which is trying to understand and make peace with her death, and with the concept of the inevitable death which we all must face one day.