a biddy according to Answers.com

a woman, especially a garrulous old one.

a psycho-biddy according to Wikipedia

a dangerous, insane or mentally unstable woman of advanced years.

In some cases, the woman may be in jeopardy of some sort, with another party attempting to drive her to mental instability.

Often (but not always), there are two older women pitted against one another in a life-or-death struggle, usually the result of bitter hatreds, jealousies, or rivalries that have percolated over the course of not years, but decades. These combatants are often blood-relatives and live a life of relative wealth.

The psychotic character is often brought to life in an over-the-top, grotesque fashion, emphasizing the unglamorous process of aging and eventual death.

Characters are often seen pining for lost youth and glory, trapped by their idealized memories of their childhood, or youth, and the traumas that haunt their past.

a pensioner - according to Wikipedia

In common parlance, a pensioner is a person who has retired, and now collects a pension. This is a term typically used in the United Kingdom and Australia where someone of pensionable age may also be referred to as an 'old age pensioner', or OAP. In the United States, the term retiree is more common. In many countries, increasing life expectancy has led to an expansion of the numbers of pensioners, and they are a growing political force.

a biddy + pensioner = a dangerous old psychotic woman, who will talk until the stars burn out about all tragic world news events, is endlessly negative, driving all those within a 50 meter radius to contemplate suicidal thoughts or murder. Spending her OAP on extending her life expectancy as well as becoming a Medicare leech, having hip/knee/heart bypass and whatever else surgery all to ensure she outlives her progeny.

Clear the spare room.. 'the biddy' is coming!