Margaret MacDonald, 55, is said to have wrongly taken the money weeks after her mother Margaret Doonin, 85, died of ovarian cancer in December 2009.
Mrs Doonin's husband Frank, a successful businessman, had died the previous year and owned a recycling company, a property firm and a pub.
But a bitter split developed in the family after it emerged mother-of-eight Mrs Doonin had removed three of her children - including Mrs MacDonald - from her will before she died.
Mrs MacDonald's husband Iain had scooped £500,000 on the National Lottery just three months earlier when a syndicate landed a £4.5 million win.
She is now being sued at Hamilton Sheriff Court after it was claimed she withdrew £86,391.86 from her mother's Royal Bank of Scotland account in February 2010. She has returned £57,000 of the £86,391 but she has been taken to court in a bid to force her to hand over the rest of the money, plus interest.
Mrs MacDonald, of Blantyre, South Lanarkshire, has claimed her mother told her to take money from the account before she died.
But her sister Frances Hutcheson, 46, of Blantyre, told the hearing: "It is total and utter lies that Margaret MacDonald received instruction from my mother to get the money for all her children. Margaret had lost her power of attorney and had been excluded from my mother's will.
"I had a very close relationship with my mother. She was strong willed and strong minded. She had an active role in the family businesses, Doonin Plant and the Doon Inn pub.
"She was good with finances, she knew everything that was going on with her accounts right up until her death."
Hamilton Sheriff Court heard that the account belonged to Mrs Doonin but other names had been added to it.
Mrs Hutcheson said: "It was my mother's account, the names of my sisters were added at different times."
She told the court that the power of attorney was given to Patricia Cavanagh and Margaret MacDonald in 2008, after her father's death.
But she said: "In November 2009, I was given power of attorney, as Margaret had estranged herself from my mother."
Mrs Hutcheson told the court that Mrs MacDonald saw their mother on her death bed, but she had missed Mrs Doonin's final moments.
Lawyer Hugh Neilson, for Mrs MacDonald, questioned Mrs Hutcheson's evidence. He said: "Knowing your mother like you do, why would she not remove Margaret McDonald's name from her bank account when she also removed her name from the will?
"If she had wanted to remove Margaret's name from that bank account then she would have done so."
The case, before Sheriff Alasdair MacFadyen, continues.