Should a 13 yr old be able to have some freedom?

Ok so I am 13 years old, I'm a girl. My parents are divorced and when they are working I am normally stuck at my grandma's house. So when I turned 12 I wanted to be able to like go out with my friends and stuff. But I am obviously "too young to be hanging out with friends unsupervised." And I don't even mention asking to be unsupervised I could really care less about that! My two best friends are (let's call them) Molly and Morgan. I asked gma if I could go to church with her every Wednesday to this Youth thing called Crossfire. It is from 7-8. My gma won't let me because she thinks I won't do all my homework and will forget about my grades. Weird? And when this friend of mine (We are not that close) Sara asks if I can spend the night on Friday go to the lake on Saturday then spend the night and go to church with her on Sunday and go out to eat it is an "Absolutely perfect idea!!" My gma ONLY wants me to hang out with Sara and it is so annoying! I want to be able to do things with my two besties and other people like go to the movies, go out to eat, or whatever but I can NOT go unless it is with Sara! And I can't stand it! And my gma denies it when my aunt tries to help me out! (She normally takes me to the movies and stuff) What should I do? It is really hard to talk to her because she thinks she is my mother and that she is always right on everything and treats me like I am 5 and won't listen to me! And I have no choice but to stay with her unless my mom or dad isn't working and when I am with them I want to spend time with them and my bro/sis. My parents both say that her house = her rules and I get that but I want a little bit of freedom .. PLEASE? If you can help I will love you forever! <333