I really want to do this, but I don`t know how to ask. Help?

I really want to become an actress. I`m 12, and have never acted before. I think I`m pretty good at it and want to audition for something. We don`t have alot of money for me to pay for anything but I live in a big city with agentcys and stuff like that. How do I ask my mom to let me? Me and her don`t have the best relationship so this could be hard!