Gail O'Rorke, has denied assisting the suicide of 51-year-old Bernadette Forde between 10 March and 6 June 2011.
Ms O'Rorke, 43, from Kilclare Gardens in Tallaght, faces three charges.
They include attempting to assist in a suicide by making arrangements for Ms Forde to travel to Switzerland.
She is also charged with aiding and abetting a suicide by helping to secure and administer a toxic substance.
A third charge concerns procuring a suicide by making funeral arrangements before Ms Forde's death.
She has pleaded not guilty to all charges.
Ms Forde died at her home in Dublin on 6 June 2011 after being denied travel to a clinic in Switzerland.
She was diagnosed in 2001 with progressive multiple sclerosis and her condition was compounded by a car accident in 2008 that left her wheelchair-bound.
Ireland decriminalised suicide in 1993 but the jury was told assisting a suicide remains an offence.
A prosecutor said Ms Forde was facing the bleak prospect of losing mobility and bodily function and the prospect of a distressing and difficult death.
He said the jury would be in no doubt that Ms Forde had made the decision to end her life and had told her family about this.
Ms O'Rorke was a part-time carer and friend to Ms Forde.
The prosecution told the court that Ms Forde had planned to travel to Zurich to end her own life and the travel arrangements had been made with the help of Ms O'Rorke.
However, the plan was abandoned when the police were notified by a travel agent.
The court heard that after the intervention of the police, Ms O'Rorke could not have been in any doubt about the law relating to assisting a suicide.
The prosecution's case is that she later assisted Ms Forde to obtain medication to end her life, the court was told.
The medication was ordered from Mexico on the internet and Ms O'Rorke made the payment and was present when the package was delivered, the prosecution said.
A recording of Ms Forde's last words was played to the jury.
In it, Ms Forde outlined how she could not continue to suffer due to her medical condition.
The court heard her say her plan to die was "me, totally me, and nobody else".
Ms Forde repeatedly expressed her frustration with the law in what she described as "this bloody country".
The case is expected to last for two weeks.
A Dublin woman has gone on trial charged with assisting the suicide of another woman, in what is believed to the first prosecution of its kind in the Republic of Ireland.