ANSWER - I don't think anyone could tell you conclusively that such a thing isn't possible. It is certainly plausible that we retain the links between close spiritual friends in our different incarnations. Nor is it unlikely that you were a witch in a previous life even though you are not in this life. However, I would not necessarily assume that just because your friend found meaning in the gift in her dream that it was given by yourself in a previous life. Dreams often bring us meaning through symbols and in this case, the gift of the dragon, symbolising strength and courage may have been a strong indication to you that your friend has found the strength within herself to face her problems and confront what was making her miserable.
I don't personally see much relevance in the dragons of the Chinese calendar, though that may just be because it's not something linked to my own path.
I think you have both got an excellent opportunity here to study what dragons mean to you and what lesson the dragons can teach you. I agree there is more to the dream for both of you, but think carefully about all the possibilities and don't assume your first interpretation of the dream is the correct one.