Judith Ducker, 64, is thought to have been assaulted during a reported robbery at Wellgate News on Wellgate in Rotherham on Thursday September 1.
She suffered head injuries and was taken to hospital, but died yesterday (Thurs October 20).
Police said a post-mortem examination was carried out this morning on Mrs Ducker, who suffered from underlying health conditions.
The cause of death is not yet known a results of the post-mortem were inconclusive and further tests have been requested.
Detectives investigating the incident have released CCTV images of a man and a woman they are keen to trace as potential witnesses to the robbery, which happened between 11am and 11.25am.
Detective Sergeant Andy Shields of South Yorkshire Police, said: “This is an incredibly sad time for Mrs Ducker’s family and friends and my thoughts and sympathies are with them.
“We are continuing to investigate the incident and we are very keen to identify and trace the man and woman on the CCTV images, as we believe they may have entered the store between the times stated and be the last people to have possibly seen or spoken to Mrs Ducker prior to the alleged attack.
“I want to make clear they are not in any trouble at all and we do only want to trace them as potential witnesses, as they may have vital information that is crucial to our investigation.
“If you believe this is you in the picture, or you know who the man and woman may be, please call police on 101, or Crimestoppers anonymously on 0800 555111, quoting incident number 388 of 2 September 2016.”
A 36-year-old man Rotherham man was charged with attempted murder and robbery on Monday September 6.
Paul Storm Blueitt, of Cambridge Crescent, Rotherham, appeared at Sheffield Crown Court on Monday October 3 and was remanded into custody until his next court date.