I totally sympathize with your situation. If you are 18, you are not “growing up too fast”, you are “grown up”. It’s unfortunate that your parents won’t let you make your own mistakes. I don’t think that you are ungrateful at all. I think that your parents are being unreasonable.
Ok, so you have this situation. People say that your choices are to dorm with sister, or commute, but there are other choices, move out and get a job, or join something like Americorps, FEMAcorps or City Year where you get to do some form of community service in exchange for a stipend, room and board. If it appeals to you, you could join the military, but if it doesn’t don’t do that.
What do you want out of college academically, what are your aspirations?
If you’re going to college for some particular mission (like a preprofessional program that you want), go and dorm with your sister and just sleep there. (I assume that you are female or it would be really weird). If you don’t have particular plans for college but want the independence, maybe considering delaying college and apply to a program like Americorps or City year in a distant city. This will give you the independent life that you crave, and will also eventually condition your parents to understand that if they want to have a relationship with you, they have to let you live independently.