To dream of your mother dying is not a warning about her death. Rather it asks you to let some negative aspect of yourself die, so that a more positive one can find expression. The negative aspect is connected with your mother, and is one that you either copied or developed as a result of your relationship. It does not matter if your mother is already dead or you have not seen her in many years. It is the effect you are carrying today that is the target of the dream. Female energy is affected by your relationship with mother and allows you to forgive, lead, listen and therefore have two-way communication. It also shapes your philosophy of life and more. The dream can be about any of these.
A dream including your mother is likely a comment on your relationship with her and how it is holding you back in some area of your life now. Dreams only focus on problems in your life. Although you may have had a wonderful relationship, there are still often traits or attitudes you copied, or an influence you allow that you could do without.