My DD, who is 9, says that she likes to play by herself and her brother most of the time, but every once in awhile I catch her talking about maybe having someone over for a playdate (which we did more often when she was younger and at our local brick and mortar school). I've struggled with teaching her some of the nuances of conversation, because frankly, at age 9, it's a lot harder to navigate than at 6 years old.
Yesterday, I found the American Girl series book "A Smart Girl's Guide to Knowing What to Say - Finding the Words to Fit Any Situation". The book is by Patti Kelli Criswell and contains nice, colorful illustrations byAngela Martini. I like that the text is done primarily with conversation "bubbles", so it doesn't look daunting for kids who don't like reading "textbooks". Also, the book can be skimmed by topic ("asking for what you want", "sad times", "what to say if someone takes advantage of you", "how to give a compliment", etc.) for easy reference. The illustrations make the book interesting and while I find it difficult to discuss some issues with my daughter because she doesn't like seeing my facial expressions change too much, the illustrations provide just the right amount of context for the "lessons".
There are conversation exercises a parent, guardian, or child can do within the book. And while the text is geared more toward middle school kids, I could see older girls and even boys benefiting from this (they aren't gender-specific for the most part - just common courtesies).
I found this book at my local Michael's (craft store), but I think I saw it online at Amazon and at Barnes and Noble.
My DD enjoyed it so much she plopped down in her bean bag and started reading it as soon as we got home. I think the text is presented in a very approachable way.
Hope that helps someone!