Not everyone can be a mother, that is for sure.
It’s not because you gave birth that you can call yourself a mother. There is more to that. Being a mother = ultimate sacrifice that a person can give. No prejudice, no taking into accounts what you have done and have given; just unconditional love. And when you cannot give that, I don’t think you can call yourself a mother.
A person need not bear a child to be called a mother. It’s the act of loving and caring unconditionally, that is.