Belfast Magistrates' Court heard Catherine Strong subjected the elderly victim to a drunken attack as she lay in bed at their home in the city.
Strong, 49, of Argyle Street, Belfast, pleaded guilty to common assault on her mother.
She also admitted five assaults on police officers and police representatives.
When challenged by care workers who called at the house she was said to have become abusive and repeatedly shouted that her mother was dying.
Ordering full reports before she passes sentence, District Judge Fiona Bagnall said: "If those care workers had not come in goodness knows what might have happened."
A prosecution lawyer told how one of those who called at the home on 10 January had looked into the area where the victim's bed is located.
She saw the pensioner - believed to be in her late 70s - lying on her back with her feet hanging off the edge of the bed onto the floor.
"The defendant was standing over her mother holding a pillow in one hand," the prosecutor said.
"She was repeatedly striking her mother on the face and upper chest with the pillow."
The assault was said to involve pressing the pillow down on the victim's face for up to a second at a time, before lifting it up for the same period of time and then repeating the action.
In total the incident witnessed lasted for less than 30 seconds, the court heard.
It was stressed that the care worker believed Strong was beating her mother, but was not trying to suffocate her.
Strong, who was described as pleasant when sober but abusive when drunk, had been in an emotional state in the previous weeks.
She had repeatedly stated that her mother was dying, Judge Bagnall was told.
During the commotion at the house she also claimed she had been trying to put a pillow behind her mother's back.
She has cared for her mother since she had a stroke 12 years ago.
On the day of the incident Strong had drank a litre and a half of cider, but claimed to be more tired than drunk.
Strong also insisted she had a good relationship with her mother involving the pair joking and messing around, the court heard.
After hearing the details Judge Bagnall stressed the seriousness of the offence against a "vulnerable, elderly lady in care, a member of the family".
Pointing out that immediate custody could be imposed, she warned: "Be under no illusion, I'm taking this as having a fairly sinister set of facts."

In June, the government in England said agency spending was to be capped and it has now unveiled details of how that will work.
From April, NHS trusts will not be able to pay more than 55% more to agencies than it costs to pay a member of staff for a shift.
It comes amid mounting pressure on NHS finances.
Figures released last week showed trusts had overspent by £930m in the last three months - with agency spending highlighted as one of the biggest factors.
Ministers believe the move will save £1bn by April 2018 - the equivalent of shaving 10% from the £3.3bn annual agency bill.
Reports have emerged of agencies being paid thousands of pounds to supply nurses and doctors for shifts.
The new limit will start to be phased in from November - with the "shift rate plus 55%" limit kicking in in full from April.
Agencies are being allowed to charge more to reflect the costs they face in terms of administration and National Insurance contributions.
Health Secretary Jeremy Hunt said: "For too long, staffing agencies have been able to rip off the NHS by charging extortionate hourly rates which cost billions of pounds a year and undermine staff working hard to deliver high-quality care.
"The tough new controls on spending that we're putting in place will help the NHS improve continuity of care for patients and invest in the front line - while putting an end to the days of unscrupulous companies charging up to £3,500 a shift for a doctor."
A woman who repeatedly pressed a pillow on her stroke-victim mother's face has been warned she could be jailed.
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Ministers have set out details of how they aim to save the NHS £1bn on agency staff costs over the next three years.