I think that one of the fundamental issues coming out of this question has to consider the time period of the work. Hansberry writes her work at a time when women were not able to fully assert their own identity and actively embody their own sense of freedom and choice. In this, women were seen as having to conform to a patriarchal notion of the good. To this end, I don't see how Beneatha can be seen as a stereotype. She is shown to be a very headstrong woman, who is able to exercise her own freedom in her choices and the identity that she wishes to embrace. This is fluid over the course of the play, and even reflects a lack of complete totality in her choices. In this, Beneatha is radical because she is a woman who will define herself and not allow others to do so. This might be stereotypical by modern standards. Yet, this could not be seen as stereotypical of women during the time period. Beneatha is a character that is one who cannot fit into any box. She is conscious of this, and in the process, she really does not embody the stereotypical notion of women.