Nobody knows what was said between the two people aboard the aircraft after it had departed. It is not uncommon for someone to be apprehensive about a flight and insist before departure that they want nothing out of the ordinary in terms of manoeuvres. Once they have been up for while they find that they enjoy it and want to push their experience a bit. Then a 'No aerobatics, please' statement heard by others before boarding might become a request for or no objection to a more energetic manoeuvre. I think it highly unlikely that Kevin would have embarked upon any such manoeuvre without the prior agreement of his passenger.
It is unfortunately a sign of the times that this country often has a blame attitude such that 'someone has to pay'. In this case, the two people involved in this accident paid the ultimate price, and those left behind should let them rest in peace and let time heal the loss, without dragging it all through a legal process which will in all likelihood make only the lawyers rich as nobody can prove whether the consent of the passenger was or was not given prior to entering the fatal manoeuvre.