The family members were asleep at the time, while Ms Walshe’s friend was at a New Year’s Eve party and didn’t hear her phone, Ms Ljubicic told Fox News from her home in the Serbian capital of Belgrade.
“And now, I regret not getting the phone, because she’s disappeared,” Ms Ljubicic said.
Ms Walshe was last seen at her home in the coastal city of Cohasset in the early hours of 1 January, authorities say.
She had been due to take a ride share car service to Boston Airport that day to return to Washington DC, where she worked in real estate.
She was reported missing by concerned colleagues on 4 January after she failed to show up to work.
Her husband Brian Walshe, a 47-year-old convicted art fraudster, was arrested on 8 January and charged with misleading investigators about her disappearance.
Ms Ljubicic told Fox News said when they spoke a week earlier on Christmas Day, her daughter had asked: “Mama, come tomorrow”.
“Which means that clearly, there must have been some problems,” she said.
Ms Ljubicic suggested she plan a visit for the New Year, but her daughter said not to worry.
“And now I can’t forgive myself for not just letting things fall where they may, and just go, and whatever happens to me, happens,” she said.
In a 9 January criminal complaint affidavit, prosecutors said they found blood and a knife in the basement of the family home.
They further alleged that Mr Walshe visited a Home Depot on 2 January wearing a black surgical mask, black gloves and bought $450 worth of cleaning supplies using cash.
Investigators said Mr Walshe had said during interviews he had visited a smoothie bar, a Whole Foods store and CVS but had neglected to mention the Home Depot trip.
Mr Walshe’s cell phone data also showed he had visited other locations around Massachusetts that day despite being under home confinement orders while awaiting sentencing on art fraud.
On 9 January, police searching for Ms Walshe discovered blood, a hatchet, a hacksaw, a rug, and cleaning supplies at a transfer station in Peabody.
Mr Walshe is being held on $500,000 bond after being charged with misleading police during their investigation into his wife’s disappearance.