I absolutely hate the fact that kids aren't allowed to choose which parent has custody over them... i was also 7 when my parents got a divorce, but i'm 16 (17 in a month) and my mom has full custody. Which is the worst thing ever... I'm only allowed to drive my car, that my DAD bought for me to school, work, and home. My dad doesn't care where i drive, and he doesn't think its fair but since my mom has custody its what she says goes and not what he says even though he paid for the car... so if i want to go hang out with my friends, i have to find a ride because my mom won't take me and i'm not allowed to drive. i pay gas and insurance and my mom's name isn't even on the papers we signed to get the car. she shouldn't have any control over it whatsoever... UGH
ETA: that's just one of the things she does. this is basically the same with everything my Dad buys me..
I do not know all of your story, but I do not believe it has anything to do with being able to pick your parents. If your parents were not divorced, your mom would more than likely have the same rule. From the example you provided, it sounds like your mother is very strict. I am a strict mother as well, not quite as strict as your in this situation, but stirct. And it is because we love and care. I purchased cars for both my daughters and they are not allowed to drive certain distances, no more than 2 people can be in the car with them. My oldest daughter is 19 and she is allowed to go out on the weekend, but if she is going out to a club with her friends, someone else has to drive and she gets really upset because "it is her car" well, "it is my house and my rules". She gets upset because she is the only one that has a car....well right there that should tell you something.
I remember hating my mother for doing similar things, being too strict and she would tell me that some day I will thank her....and being my rebellious self, I swore that even if I felt that way, I would never tell her.....Well now that I am a mother, even before, as I watch how my life turned out so differently than my class mates, I thank her....I thank her for her rules and restrictions that I hated soooooo much, because them made me the wife and mother that I am today.
You can not see it now, but you will in the near future and you will thank your mother!
I know I went on forever, but I think this is something that every teenage girl goes through with their mother, and in most cases, it all turns out okay.
Good luck