Below is the original casting call:
[SARAH COMPTON-HARRIS] Female Caucasian 70s – 80s. Seen in a flashback to 1931, the elderly, very frail Sarah has been ravaged by cancer and is close to death. One day guest star (11)
And, here’s the revised casting notice that changes the age of a character:
TRUE BLOOD, Episode #508, “Somebody That I Used to Know” (Revised Role of Sarah) Start Date: approx. 4/2/12
[SARAH COMPTON-HARRIS] Female Caucasian 40-45. Seen in a flashback to 1931, in a scene with Bill (Stephen Moyer). One day guest star (11)
That’s an interesting change. She can’t be Bill’s daughter unless he made her a vampire around 1900. If she’s human and 40-45 in 1931, then she could be his granddaughter or maybe his niece. This revised casting notice doesn’t mention anything about her being sick or near death.
source: IMDB.com