You and your husband are both examples of helicopter parents. You have made your daughter the focus of YOUR lives, instead of allowing her to grow up and LIVE HER LIFE. No wonder she's immature. You're not letting her BECOME MATURE. The more you try to "protect" her from experiencing real life and the real world, the more immature and socially backward(not to mention rebellious) she's going to become. You and your husband need to learn to LET HER GO. She needs to go to events like slumber parties, and host a few herself. As long as the only contact she ever has with other kids her own age is at school, she'll going to be way behind socially and may even become a target for BULLYING. Kids get picked on when they don't have social skills or they dress, speak, or act in ways that aren't considered acceptable by their peers. When I was your daughter's age, I was in Girl Scouts. That was a wonderful experience for me, and I still have lots of memories from it. I got to do lots of things with my scout troop. We went on camp outs, excursions to places like museums and parks, and we did a lot of service activities too, such as going to local nursing homes during the holiday season to visit the residents and sing Christmas carols for them. I also remember that my troop hosted a few afternoon tea parties, and we invited all the moms from our troop and another troop to attend. Those tea parties were a lot of fun. We learned a lot about etiquette and how to dress properly for such events, as well as how to do introductions and make polite conversation. These are examples of social skills that YOUR DAUGHTER needs to learn too, only it's impossible for her to do so right now because you won't let her. How many 6th graders do YOU KNOW who know how to properly introduce an adult in a social situation? I'm guessing probably very few. Social graces are SO important, for both girls and BOYS, but schools these days don't teach these skills.
Your daughter would benefit ENORMOUSLY from being involved in Girl Scouts or a related activity. And she'd also benefit from being involved in SPORTS, or perhaps the performing ARTS, such as music or dance. Research has shown repeatedly that girls who are involved in activities like sports, ballet, music, etc., have far fewer issues with body image and self esteem, and are much less likely to engage in risky behaviors like pre-marital sex than their uninvolved peers are. That's because these activities help girls learn to cope with peer pressure, and they teach skills like how to be a team player, communicate well, listen well, and so forth. I loved being a scout when I was young. I'm sure your daughter would enjoy that too, but you have to give her the chance to do it. Or if she's not into scouting, then encourage her to find another interest. Let her take piano lessons or go to dance class. If she has a sport she likes, let her take lessons in that. For me, my sport was and always has been horseback riding. But there are plenty of other options for girls your daughter's age.
Having a 9PM curfew on school nights isn't unreasonable. In fact, it's a good way to encourage your daughter to develop healthy sleep habits. But you need to quit putting so many restrictions on who she can be friends with. She needs more than just one friend if she is going to develop normally and have a healthy emotional outlook. And that may mean you'll have to take the bitter with the sweet and accept that you won't necessarily like the parents of the friends your daughter chooses. I had people I hung out with when I was young who my parents didn't care for either, but that didn't stop me from getting to know them.
About the homework issue- the best way to deal with that is to allow the law of natural consequences to work. This means you quit reminding your daughter to do her schoolwork. If she doesn't do it, or she forgets it, or she fails a test or two because she hasn't studied, the embarrassment of that (not to mention the embarrassment of getting poor grades and having her privileges taken away) will be MORE THAN ENOUGH to convince her of the value of doing schoolwork on her own. Let the punishment fit the offense. If she doesn't do her schoolwork, and her grades drop, she loses her privileges. She doesn't get to do fun things any more, until she gets her work done. And don't be afraid to REMIND HER that having and being able to use a tablet, a smartphone, and Ipod, etc, is A PRIVILEGE, NOT A RIGHT. One of the things your daughter needs to learn is that if she ABUSES her privileges, she will LOSE THEM. That will help to stop her from thinking that the world owes her a living, and that life revolves around her.
One last note before I end: Your husband needs to quit driving your daughter to school, period. She either needs to walk or RIDE THE BUS, just like every other kid her age does. It's insane that he wastes time and gas driving only 3 blocks twice every day, not to mention the wear and tear on the car. There are a ton of parents around where I live who do the same exact thing, and it drives me NUTS. What a waste of time and gas. These kids need to learn to ride the school bus. That's what the bus is for.