At 12U my DD just had a fastball and an okay change up. I would recommend just focusing on mechanics and how to command those two pitches. It will pay dividends later. I used to laugh at other dads who said their DD had a curve ball at 11 or were working “on a rise.” I caught bullpens for all these girls. They had fastballs. Almost none had a change up.
Later, my DD added a drop ball (same mechanics as fastball) and just to make @Hillhouse’s head explode, a screwball. My DD is not a hard thrower, but has got a lot of circle time—including now in HS as a Freshman on varsity—because she can hit her spots and move the ball. If you don’t know where the ball is going when you throw it—no matter what the pitch is—you are ultimately not of much use.
Later, my DD added a drop ball (same mechanics as fastball) and just to make @Hillhouse’s head explode, a screwball. My DD is not a hard thrower, but has got a lot of circle time—including now in HS as a Freshman on varsity—because she can hit her spots and move the ball. If you don’t know where the ball is going when you throw it—no matter what the pitch is—you are ultimately not of much use.