After writing the above, on impulse I Googled Charlie Stone-Wigg's name, and to my horror was referred to this: http://www.timesonline.co.uk/tol/news/world/article1008865.ece

Charlie and Ann had survived an almost identical attack, when their bedroom was invaded by Mau Mau terrorists in 1959, which, as the article says, cost Charlie his eye, but his assailants their lives. Evidently the bedroom door was not locked this time.

I have emailed Ann's sister, Verity Williams, to try to find out whether Ann recovered.