How about buying her a book on Gentle Parenting that includes a section (or more) on encouraging positive behaviours and discouraging negative ones in a gentle way. I'm sure there must be something out there that does this. She might even thank you for it because she probably doesn't want her son to be avoided but just doesn't know what to do differently without seeming too harsh. You could explain to her when you give it to her that you too believe in gently parenting and understand how difficult it can sometimes be to know how to go about certain things. And that sometimes things that seem gently might not be - ie ignoring bad behaviour isn't gentle at all because it causes low self-esteem just as much as harsh discipline, and that it will ultimately lead to an unhappy child that no-one wants to play with. Of course be subtle in the way you word that!