Sabina Marsden, 78, was slapped, shouted at and had a blanket snatched from her lap.
The horrifying assault was captured by a hidden camera in Mrs Marsden's home just minutes after it was set up on June 13 last year.
Mrs Marsden's daughter Gina Owen, 46, said: “Within 10 minutes of Mandy [Gina's sister] leaving the house I was watching it on my phone and she slapped my mum four or five times.
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“We only put the camera in because we thought she was being lazy.
“I didn’t expect to see that, I was shocked. I felt sick.”
The carer, 46-year-old former Mega Care employee Stacey George, was given a caution by police after admitting the assault.
When she was challenged on the hidden camera, she said: "I didn't mean to upset you. I'm sorry."
But Gina said justice had not been done.
She added: “If I hit her that day I would have been a lot worse off than her.
“She shouldn’t have got off with a caution.”
Northamptonshire Police said they would meet the family to discuss their decision if they wished.
A force spokesman said: “We can confirm that we investigated reports of an assault in Kettering which took place on June 13, 2017.
"After a thorough investigation and a review of all the evidence, a 46-year-old woman was issued with a police caution.
“Safeguarding vulnerable people is a high priority for the force.
"It’s disappointing when victims and their families are not completely satisfied with the outcome of an investigation and we would be happy to discuss this with them if they’d like to contact us.”
Miss George worked as Mrs Marsden's carer for her Kettering-based employers for almost two years.
The family brought in carers after the death of their father Malcolm, known as Mick, in August 2015.
Gina said that there was a notable decline in her mother's health.
She said: “We thought her decline was just her dementia.
"You used to walk in and she would grab hold of your hand really tight.
"She used to scratch her legs constantly."
Mrs Marsden's eldest daughter Mandy Aston, 48, said she felt like they had let their dad down.
She said: “Looking back at it now you think was she trying to tell us something?
“We promised our dad when he died that we would never put mum in care and we feel like we’ve let him down."
Since the assault, Mrs Marsden's health and well-being has improved and she is talking more than she did and sleeping better.
Both Gina and Mandy criticised Miss George's employers and made a number of allegations about the quality of care they provided and their response to the assault.
Mega Care's chief operating officer Winner Lawal said they were 'gravely disheartened' by the allegations and that all of their staff are trained to the level set out by the Care Quality Commission (CQC).
Mr Lawal said: "We are appalled and disgusted by the actions of this ex-staff member.
"Of the 22 months that we cared for Sabina, this same staff member provided more than 96 per cent of the total visits.
"Sabina was the only service user cared for by this [member of] staff.
"Regular feedback from Sabina’s daughters expressed their preference of having this staff member as their sole care worker.
"We believe in the importance of continuity and understand the benefits continuity can have in the lives of our service users, therefore we agreed to this request.
"There was no prior indication that this staff member was capable of these heinous acts."
Since the incident, the family of Mrs Marsden say they have received a bill from Mega Care which they are refusing to pay.
A spokesman for Seatons Solicitors, which is acting on the family's behalf, said: "As lawyers at Seatons we are, sadly, no stranger to cases of elderly abuse.
"It is really important for families of the elderly to watch out for signs that there may be problems, as this family has - particularly where the elderly person has a vulnerability such as dementia.
"The legal framework for the protection of the elderly is not as robust as it needs to be.
"That the carer in this matter has been dealt with by way of a caution means that she has admitted the assault.
"Had this been a domestic assault, or if the victim had been a child, I strongly suspect that the assault would have elicited a much harsher, and in my view more appropriate, response from the criminal justice system.
"Unbelievably since the assault our client has received a bill from the agency providing the carer.
"Seatons will continue in our efforts to hold those responsible for the failings in the care provided to Mrs Marsden."
Had Gina and Mandy not put up the camera , which they only did after advice from a second independent carer, the assault may never have been discovered.
Mandy urged anyone who suspects any form of abuse from someone in a position of trust to do the same.
She said: "If anyone has an inkling they need to shout because otherwise, people are going to get away with it.
“I think there’s probably more people out there that this is happening to and they’re either too scared to come forward or they haven’t got the evidence.”
An earlier version of this story included Mr Lawal referring to a CQC investigation. The CQC have since told us that they do not carry out investigations into incidents, only inspections.