Is it possible that the provider runs a preschool program and only enrolled summer clients that would be staying on for preschool? If she took this family over a "more stable" enrollment she would be making a business risk management decision. That is a lot of lesson plans to write, in vain, after all.
Maybe the termination is more about the disrespectful behavior of the kid causing issues with the group than the "threat".
I am curious, why did this client leave you OP and are they now coming back? Why are you choosing to be involved?