I am thinking that the doll might be a little earlier than the 40's/50's since making a "Mammy" doll would have fallen out of popularity by the end of the thirties I think. Others may want to comment on this, but I think that even if it was made for an african-american child during that time, it would not have been given the headscarf and such associated with characters like Aunt Jemimah. She clearly has that look and I think you could also describe the doll as "black americana", which might help generate interest. I am betting that if the fabric has an old, worn feel to it that your doll is 20's or 30's.