Family Issues Support Group
Family issues is a huge range that go from minor conflict to major misbehaviour and even abuse on the part of individual members of the family occur. Whether you feel you are in a dysfunctional family or you're dealing with a very specific issue, this is the place to talk about it and find others who might be going through the same thing.

That sounds harsh but true.
At the same time, outside of her negative comments. Since you will be hours away, this may be the real reason she is against it. Your friends are simply going to miss you. But, a heed of warning, just make sure you listen to their comments and aren't being swept away. Hopefully they aren't seeing a bad situation before it starts that you're missing.
I'm guess the truth is, they are all going to miss you. But, you are your own person, entitled to YOUR own life and happiness.
She has no right to demand anything of you, it is wrong of her to do so. I think you should deff. move out. Sounds like you have been slave to her for years and she has taken great advantage of you. What do YOUR friends say?
Think about it, it is time for you to have a life and find out what you want to do with your life besides take care of your sister and her family. How about a family of your own!
Good Luck
And to tell you that you can't move out?! She is sooooo using you it is sickening!!! and I can't believe you are falling for it!