Fred Payne, 78, allowed Lisa Connelly to stay at his home in Rochdale Way, Colchester, where she "dominated him" and helped herself to a "sizeable" chunk of his pension, a court heard.
She started a fire in the bedroom of the flat last September.
Connelly, 42, admitted manslaughter and arson charges.
Chelmsford Crown Court heard her life had fallen apart at the age of 30 when she got into drugs.
Mr Payne, described by neighbours as a lovely man who wouldn't hurt anyone, had taken Connelly in, and she repaid him by neglecting, exploiting and manipulating him, the court heard.
She had been sleeping in the bedroom of his flat - where he had lived for 20 years - while he lived in the living room.
As his health deteriorated, Connelly had taken a sizeable amount of his Â£260-a-week pension to fund her drug habit, buying mainly crack cocaine.
The court heard Mr Payne, who had no traceable family, had cocaine in his system when he died as a result of inhaling smoke.
Two heroes, Dale Copping and Anton Cook, had tried to save Mr Payne from the burning building.
Mr Cook had gone through flames three times in a bid to help him, but was unable to find him.
A 96-year-old woman was saved from another flat.
Connelly had previously admitted a separate offence of burglary, but will serve no further time for that.
A drug addict who "exploited and manipulated" a pensioner for his money before starting a fatal fire at his flat has been jailed for 12 years.