Re: Defiant little girl...I have to tell my friend that her DD can't play with DS any
One approach is to frame it in terms of what you allow/are capable of:
"I've realized that I can't accomplish the daily things I need to when I also need to be right by Rosie's side."
"I'm not sure what tactics you use at home, but I'm unable to convey to Rosie when I need her to follow instructions."
"I'm unable to help Rosie to enjoy her time without it leading to out-of-control behaviors that damage our property or each other."
"I don't seem to have or be gaining the authority with Rosie for her to follow orders or understand that she needs to treat our home & family as nicely as she treats her home & family (or as nicely as we treat each other, if she is just as disruptive at home)"
Puts the focus on you and your limitations, while still making it clear that the end result has been her behavior is not acceptable.
A (usually) happy wife mama to my BOGO girls, DD1 July 2010 and DD2 Dec 2011.