hi !!!
I sure would try to explain this again to your neighbour !!
try to be gentle but firm !!
say you love those kittens too , but that you do not like to have their little girl near that car again ...... just say it is because of the state that car is in .... ! Of course we all know that this in no good to the kittens and their mummy too !
no harm in trying , right !!!!!