A girl can be a "G", a girl can be anything she wants. This is a good time for you to live your life with an open mind. I don't think it's a good thing for anyone to aspire to be a "G", it's just the way you are asking your query that is disturbing, like a girl is not normal if she wants to be something that generally is what a guy is. Straighten up and fly right, make sure you think things through before creating prejudices.