Sharon Jennings was walking her own pet in Preston, Lancashire, just over a week ago when the attack happened.
The 55-year-old was bitten on the hand and neck when she attempted to defend her dog from being hurt.
She was found unwell at her home on Monday and taken to Royal Preston Hospital where she died last night, it was confirmed this evening (Saturday, June 8).
Lancashire Constabulary are still trying to trace the owner of the other dog, who fled the scene of the incident on the old railway lines in Brookfield, between 6pm and 7.30pm on May 31.
The man is described as having thinning grey-black hair and wore a blue fleece jacket.
His dog is described as “a speckled ginger-and-black” canine of medium height.
Detective Inspector Chris Wellard, of Preston Police, urged the owner or anyone with information to come forward.
He said: “Our thoughts are with Sharon’s family and friends at this incredibly distressing time.
“We’re working hard to establish what happened but need anyone with information to come forward as soon as possible.”