Thanks for your reply Dave. Believe me, everything concerning my grandmother has been a nightmare which I have battled with for years until I had a big breakthrough when the 1911 census was released a year ago. So I'm not expecting anything to be easy!
Indeed, I know about common graves as my father is buried in one in Alperton cemetery.
Thanks for the tip about Islington cemetery, I'll give it a whirl. My grandmother lived in Corbyn Street, Islington, according to the death certificate, so she might well be in that cemetery.
All the best,
Lawrence.