I hope he can appreciate that more and more... DIL may be able to justify things and he believes her (Like "it is not my fault, it is that Autumn doesn't want to go) and if you don't delve into that it might appear to be objective reasoning... but the fact that it is DIL that is keeping alive all of the bad feelings for as long as possible, that is where the mask comes off.

Even if DIL wants to claim complete innocence in this incident... there is the concept in law of "mitigating damages"... if you have a plumber over and he leaves the main on while a pipe is leaking on Friday, and you see it on Friday, you can't leave the water on all weekend and then sue him for all the water damage on Monday. Judge will throw the case out. It is your job to mitigate damages by turning the water off as soon as you notice it.

Even if DIL did nothing to instigate, it should be her responsibility as a member of the family to mitigate damages: hurt and bad feelings. She should be talking to Autumn to try to get past this and get an apology to you. Not only is she not doing that, but she is working hard to make sure that the hurt DOES last and that everyone knows it.

I hate to think of the life lessons she is teaching this child.