The only way is through puberty... unless you take some kind of hormones. Besides you should wait for puberty to hit. cause when it hits.. it can hit hard. your face breaks out in zits, you get stringy armpit hair, and your voice cracks especially when you talk to your crush.
Yes, and it involves muscular development of your throat, your rib cage and your diaphragm. I was told that a deep voice is impossible for females, but I proved that wrong. However, your throat growing in size via puberty will also be a factor in your case.
If you breathe a balloon-full of sulfur hexaflouride, your voice will temporarily get much lower. It has the opposite effect as breathing helium. But it only lasts a minute. And if you breathe too much of it, you're gonna have a bad time.