Whitney Houston's mother is still struggling to come to terms with the superstar's untimely death as the first anniversary of her passing looms, and feels "angry" her daughter was alone when she died.

The singer was found dead in a bathtub in her Beverly Hills hotel suite on 11 February (12), on the eve of the Grammy Awards, and her mother, Cissy Houston, is still wracked with guilt.

In her upcoming memoir, Remembering Whitney, Cissy details her daughter's drug addictions and the downward spiral that led to her death.

An excerpt obtained by People.com reads, "She started partying and she didn't really know how to stop. I used to wonder what she was doing at night, where she was... Could I have saved her somehow?... I'm angry she died alone, in those conditions. I'm still mad about that."

Cissy also admits she doesn't blame Houston's ex-husband Bobby Brown for her drug dependency.

She adds, "I blame him for the way he treated her, but I don't blame him for her drug problems. He was no help to her at all."

The 79 year old hopes her book, due for release on Tuesday (29Jan13), will remind fans "what a good person she was. I want people to know the truth about her, how she really was."