I really think this question means that this person is important to you, and you may see her in many different roles or places in your life.  To be your mother according to the dream may simply be a strong desire for your real mother whether you have a substitute mother or not.  Dreams can be one way of bringing to the surface what someone has deep within their minds; if it is brought to the surface by dreams, the person can begin to deal with the important information.  Because it deals with a real mother figure, you must be dealing with many questions about your real mother.  Not being a medical doctor, I would not be able to give you a real answer, but only one with ideas about what the dreams could mean.