The 42-year-old's case relies on provisions in the Bill of Rights Act enshrining the rights to not be deprived of life or subjected to cruel treatment.
One of Ms Seales' legal team Andrew Butler said whatever suicide was defined as, that was not what his client was doing.
"What she is doing is exercising her Bill of Rights rights."
A blanket ban of assisted euthanasia would also signal the courts were happy to overlook individuals' rights in favour of benefits of others.
"The end justifies the means," Dr Butler said.
Earlier today another of Ms Seales' team Chris Curran argued it should be legal for a doctor to change a saline solution from saline to a lethal substance.
The action would be in the context of a therapeutic relationship that would negate any assault, grievous bodily harm or poisoning charge, Mr Curran said.
"Context is what's important in determining whether a substance is noxious."
Doctor-assisted euthanasia "prolonged life", because in the case of Ms Seales, if she did not have that option, she would be forced to take her life prematurely while she was still physically able to, he said.
"It is dehumanising and devaluing for Lecretia to explore a secretive and lonely death."
Ms Seales was not present for this morning's court session.
Yesterday she attended periodically throughout the day, sitting in a wheelchair next to her mother and husband Matt near the front of the court, often with her eyes closed while she listened to her lawyers' submissions.
Ms Seales had been living with the diagnosis since March 2011, when a neurologist determined brain cancer after she had been experiencing headaches and loss of vision in her left eye.
Yesterday the court was told her life expectancy was weeks or "some short months".
Also joining Ms Seales' case is the Voluntary Euthanasia Society.
The Human Rights Commission and anti-euthanasia group Care Alliance will also give submissions.
The public gallery was again packed for today's hearing and a handful of Ms Seales' supporters were seated in the jury box.
The hearing is expected to finish tomorrow.