These people almost never grow up. My spoiled 56 year old brother is still a child. My mom lives with him and is still kissing his ass. He is a pathetic failure in life and of course, it's not in any way his own fault as far as he's concerned. He surrounds himself with submissive people who play his game, including his thirty-something third wife. I have no intention of ever speaking to him for the rest of my life.

I would give your sister a chance to grow up, but don't be too disappointed if she doesn't. Some family relationships are not meant to last a lifetime.