The woman, who was 75 years old when her family contacted the police in November 2010, had previously suffered a stroke and was left with a communication disorder known as aphasia that has made speaking difficult for her.
She testified at a hearing in April to determine her competency as a witness, and Sacramento Superior Court Judge Cheryl Chun Meegan later in the same month also ordered that the woman undergo a doctor's examination to further assess whether she would be able to take the witness stand at trial.
The judge found that "by virtue of (the witness') condition," that she "is not capable of expressing herself in a manner as to be understood and that no reasonable accommodations exist to assist the witness, " court documents show.
The judge sealed the doctors' reports on their examination of the woman.
Authorities identified the woman as the victim in the complaint against the former officer, Gary Dale Baker, 50. The complaint accuses Baker of rape, sexual battery, assault with intent to commit rape and other sex crimes.
Prosecution and defense attorneys could not be reached for comment earlier today.
Despite the judge's ruling, the prosecution is expected to go forward with the case that would be based in part on DNA and videotape evidence.