Yea if you were to ask the CAA this question:
a) Its take 60 days for them to get around to replying, then they would apologise for the delay
b)They'd quote a snippit from the ANO stating something along the lines of
"As a PPL you are prohibited from giving flight instruction without an FI rating"
which wouldn't answer the question.
So, its an academic question really. If I teach my Mrs to handle the controls, so if I cark it at the helm, she may stand a surviving, then thats what I would do.....
EA