very exciting.
Then did she or her family give testimonies during the 1947 War
Crime Trials in Singapore? 
The modus operandi of the Kempetai during the early part of the war
(when Sook Ching happened) was not to behead people secretly.
Moreover:
1. Beheading was an honour accorded to the beheaded. Refer to
Operation Rimau.
2. Beheading was slow, shooting and/or bayoneting is faster.
3. According to documented records, the victims in Sentosa were
taken out by motorboats, iirc, to be shot.
4. If beheading happened, e.g. first week after British
capitulated, it was done as a severe warning to the civilians.