Hmmm, lots of problems here! How about staying where you are and offering a place for your sister to come to?
To be totally honest, I do not think that you will save her from the turmoil by moving closer to her...she is 20 and is of legal age , she can move anywhere she wants to right now.
I sense that there is even more to this story, I wouldn't rush into anything.
Keep posting, it will help.