Sad to hear, although luckily Edgar Wright's film Hot Fuzz gave her, along with Edward Woodward, a memorable late role!
Here's her introduction in the film!
She had many interesting and edgy roles in her career, from an uncredited role in John Ford's Gideon's Day (aka Gideon of Scotland Yard), through to Hitchcock's Frenzy, both films that interestingly starred Anna Massey!
Lots of great horror roles in there too. Along with the evil nanny in the original version of The Omen she is also in a retelling of the Burke and Hare story in
The Flesh and the Fiends and
Twisted Nerve. She also memorably provided
the voice of Augrha in The Dark Crystal too!
There are a couple of fascinating British films that she is in that I hope get released on home video sooner or later, perhaps in the BFI's Flipside series: Charlie Bubbles, starring and directed by Albert Finney and written by Shelagh Delaney; Chris Petit's adaptation of P.D. James' An Unsuitable Job For A Woman; and John Boorman's Leo The Last, in which Whitelaw co-stars with Marcello Mastroianni.
But in terms of released films she was also great in Stephen Frears' Gumshoe and in a non-horror Hammer film, the excellent crime thriller
Hell Is A City (the title of which was apparently controversial in describing Manchester!) Plus she had a memorable supporting part in Stephen Poliakoff's
Shooting The Past mini-series. Her character also got one of the short ten minute episodes dedicated to some of the characters relating a story through still photographs, which I think I'm going to rewatch tonight as perhaps the best tribute to her.