The remaining sex abuse charges, four counts of gross indecency, one of attempted gross indecency, two of indecent assault, were 'left on the books' and not proceeded with.
Her 65-year-old stepmother and former Newtownabbey councillor, Briege Meehan, was to have gone on trial at Belfast Crown Court on Wednesday accused of a total of eight charges, seven of sex abuse and one of child cruelty.
However, before the jury of eight men and four women could be called to hear the case, prosecution QC Frank O'Donoghue successfully applied to Judge Gordon Kerr QC to amend the indictment by adding two counts of assault occasioning actual bodily harm.
Mr O'Donoghue said these charges were committed over the same 15 month period from 14 July, 1979 and October the following year.
One alleged that Briege Meehan, from Elmfield Street in north Belfast, struck her stepdaughter Mary on the head with a bottle, while the tenth count accused her of injuring her either with a brush shaft or a shoe.
Defence QC Karen Guinlivan in turn asked for the count eight cruelty charge - that she wilfully assaulted and ill-treated her stepdaughter in a manner likely to cause her unnecessary suffering or injury to health - and the two additional charges of assault, be put to Meehan.
When later asked for her pleas to the charges, Meehan replied: "I plead guilty".
Mr O'Donoghue told the court that he had consulted at length not only with the DPP, but also with the victim and in the circumstances of the three guilty pleas, there "was no need for a trial" on the first seven counts of sex abuse and that they be 'left on the books'.
Meehan was released on continuing bail by Judge Kerr before sentencing next month.
However, the judge warned her that she should not take her release as an "indication of the sentence to be passed."
Briege Meehan, was the then girlfriend of Martin Meehan, when the offences were committed.
He was on remand in prison on IRA kidnapping charges for which he was eventually jailed for 12 years.
Mr Meehan, who died in 2007, was also the first person to be convicted of membership of the Provisional IRA.
Briege Meehan, his second wife, was elected as Newtownabbey's first Sinn Féin councillor in 2001, and again in 2005.
She was suspended from the post after the allegations of abuse first surfaced in February 2009.
Later in a statement, her stepdaughter said the three guilty pleas were a vindication, silencing those who accused her of being a fantasist.
The statement also read that she hoped they would now bring closer to what had been a devastating part of her life.