Of course she wants to be a princess. She is a four your old girl. My daughter wanted to be a princess at 4, too. Today she is 12. In a STEM focused school and just did her seconded FLL Lego Robotics competition. She is active in her school's TSA (Technology Student Association) and competes in various science contests. She is two years ahead in math and wants to pursue a STEM career. Her favorite color is pink; she likes to wear dresses and did all the girl related toys. It is ok for a girl to like princesses and pink and all the frivolous stuff. Dolls don't turn you against science and math.
But we also pushed science related stuff on her early. We bought lots of those science kits for kids and did them with her. Dumped a ton of lego’s on her. I spent many evening building lego’s and doing science kits and physics kits and volcano kits and walking fields, looking at rocks, ect. What you need to do is spend time with your daughter at an early age doing science kits, and looking at the environment and poking at rocks and asking questions of her to get her to think. As a dad, best think you can do is spend time with your daughter and guide her to thinking about her surroundings and what not. But don’t take away the girly toys; Let her be a girl because it’s ok to be a girl and be into science and technology. Don’t think you need to turn your girl into a boy to get her into science.