How do you teach a 10 year old social skills?

Evidently, the way I have been going about it is not sinking in because LG is having big problems.  Case in point, over the weekend she had a friend overnight on Saturday.  This is a friend that she has had since she moved into our home.  They must have gotten in at least 5 tiffs.  I classify these as times when LGs friend didn't do what LG wanted her to do, and LG skulked off in a huff and left this girl behind.  Jerry and I both try and help walk her through how to deal with fights with friends.  That's not the only thing that has come up concerning social skills.

She also doesn't know phone ettiquite, what's appropriate in public, and being a gracious host. This weekend I don't know how many times I had to tell her that something was not appropriate.  She had a friend stop by, and she asked the friend in a snotty way, "Why are you here."   I know that she's learning, but why doesn't she understand that if her friend came over she wants to play, or spend time with her.  I feel like the things we are telling her are not sinking in.  I guess time will tell, but I hope that she learns, because it gets a bit embarrassing sometimes. 

Any ideas would be greatly appreciated.  We have gotten her into girl scouts, and try to let her interact with friends and family as much as possible, but it's almost like people don't hold her to the same standard because they know about her situation.  I wish they would treat her like the would treat other children behaving the way she does, so that she would learn.

It doesn't help that I was brought up to have excellent manners by my grandmother and all other adults.  Now, I have no patience for bad manners.