I agree, MysteryReader, there isn't very much on the death of Rebecca; especially detailed information. However, I did find several interesting things during my research:
Innocent CORNELL was Lizzie’s great, great, great, great grandmother.
Sources:
http://tinyurl.com/lm8j677 and
http://tinyurl.com/l2jfdso
Descendants of Richard Borden and Innocent Cornell:
http://tinyurl.com/l4nn8kn
Genealogy of the Cornell family : being an account of the descendants of Thomas Cornell
(
Hint: To turn the page, just left click on the page to the right).
http://tinyurl.com/pnbclka
The story of Rebecca Cornell, based on Occhi's recounts, begins on a cold night in February, 1673. Rebecca, the matriarch of the family whose husband had died years back, was 73-years-old. In the 1600s, to live to the age of 73 was quite an accomplishment, according to the Valley Inn operator. "Seventy-three back then is probably the equivalent of 100 today," Occhi said. Rebecca lived in the house she owned with her son, Thomas, and his wife, as well as their two daughters and four sons from a previous marriage. That one particular night, Rebecca "didn't feel quite right and chose to not have dinner with the family," Occhi said. She retired early to one of the bedrooms on the first floor. To this day, no one knows exactly which room she visited, Occhi said. A little while later, Thomas and his wife heard a noise. They went to check on Rebecca, who was found in her room dead on the floor. "It appears she had tripped and fell into the fireplace," Occhi said. Rebecca was found lying halfway in the fireplace, partially burned. Read more at: http://tinyurl.com/n9vhoyh
Today's Valley Inn Restaurant stands where this unusual murder case took place—the only case in U.S. history where "spectral evidence" or ghost testimony offered at trial resulted in the conviction and hanging of the accused killer. One cold winter night in 1673, Rebecca, 73, was found dead on her bedroom floor lying halfway in the fireplace, partially burned. Did her adult son Thomas Cornell kill her? An unusual witness accused him as such, and right up until his execution, he proclaimed his innocence. Read more at:
http://tinyurl.com/pr492cb
The house in which Rebecca Cornell died. … Her room was on the first floor to the left of the entry. (
Hint: Click on the book cover to look inside, and then scroll down to the first page, which starts with a picture of the house on it):
http://tinyurl.com/m5j35s8
Thomas received a fair trial in the context of his era. What was strange was the outcome, given that "the odds" were in Thomas’s favor (49): homicide convictions were rare, the evidence against him was entirely circumstantial, and the defendant’s high status as a frequent town officeholder and former legislator made him a likely candidate for clemency, if convicted. Yet after the trial jury brought in a verdict of guilty and the judges pronounced a sentence of death, Thomas (all the while protesting his innocence) declined to petition either the legislature or the crown for clemency. Hence the forty-six-year-old swung from the gallows on May 23, watched by a crowd of a thousand.
And yet the legal actions did not end there. One year later, Wickopash, an Indian who had been a servant in the Cornell household in 1673, was indicted for abetting the murder. We know only the bare bones of the proceeding: He pleaded not guilty and was acquitted by a jury of nine English settlers and three Native Americans. In late 1675, one of Thomas Cornell’s brothers, suspicious that Thomas’s wife Sarah had had a hand in their mother’s death, initiated a highly unusual private prosecution against her but then failed to bring witnesses or make good the charge when the time of trial arrived. Sarah herself had already publicly declared her own verdict in her husband’s case: when she gave birth to Thomas’s posthumous daughter, Sarah named the child Innocent.
Source:
http://tinyurl.com/l2del8b
Whereas you Thomas Cornell have beene in this Court, Indicted, and Charged for Murdering your Mother Mrs Rebeca Cornell Widdow, and you being by your Peers the Jurry found Guilty, Know, and to that end, prepare your selfe, that you are by this Court sentenced to be carryed from hence to the Common Goale, and from thence on ffryday next which will be the 23th Day of this instant month May, about one of the Clocke, to be carryed from the sayd Goale to the place of Execution, the Gallows, and there to be Hanged by ye neck untill you are Dead Dead.—
Source, Trial of Thomas Cornell for the murder of his mother, Rebecca Cornell:
http://tinyurl.com/ptdlgsm
Did Thomas Cornell murder his mother?
Certainly he wasn’t the only one who had the opportunity to do so; the house was full of people that night. In fact, a year after Thomas’s death, the servant Wickopash was tried as an accomplice to the murder. Nothing is known about the case against him, but he was acquitted.
In 1675, Rebecca’s son William tried to make a case against Thomas’s wife for the murder, but he failed to produce any witnesses or evidence against her.
Source:
http://tinyurl.com/ozrvqfd
Here is a picture of the Cornell Family Homestead that was in the photo section of the Find-A-Grave write-up on Stephen Cornell, who was the brother of Innocent Cornell Borden. Source:
http://tinyurl.com/nrnqmfz :
Cornell Family Homestead - Portsmouth RI-1700.jpg
Here is the site of the Cornell graves:
Cornell Grave Site.jpg
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I can't find anything much more than what I wrote. One of her sons tried to find witnesses or evidence to say Sarah had something to do with the murder (this was 2 years later) but there wasn't anything. I have one website saved where one of her (Rebecca's) daughters give some insight into her mother. Rebecca at one point talked suicide but she was religious and didn't want to do it so that is one of the choices people say happened. 
Then again, Lizzie isn't the one who ended up at the end of a rope despite her being unable to torch the place.
