Advice,

Don't argue with idiots.
They will take you down to their level, and then beat you with experience.

Another poster offered this advice to me a few months ago, and I have it taped on my office wall right behind my computer so I can refer to it every day. It's the truth.

You're doing the right thing. Take the high road. Ignore their snide comments. Getting involved in it will only bring more heartache to the situation. And, if this girl doesn't realize that 4 and 6 year olds fabricate all sorts of stories, she's not too bright.