Do you think it's natural for an 11 month old baby to call you "Mama" by herself? ?

Up until 15 months old a baby does not place who they are calling mama or dada. A baby raised with no father in the picture may still say dada, just because it is one of the first sounds. It is between 12 and 15 months when they actually start referring to their parents as mama and dada. You could try just referring to yourself as "DeeDee" as that will be easier for her to say.