But on Friday, a judge indicated he will dismiss the lawsuit, saying it's not his place to change state law, according to the Associated Press.
"If new law is made it should be by the Legislature or by a ballot measure" or from a higher court, San Diego Superior Court Judge Gregory Pollack said during the hearing.
"[Y]ou can't get it from a lower level Superior Court judge like me," he said.
He said he will issue a written ruling Monday but expects it to be appealed.
O'Donnell, a former Los Angeles Police Department sergeant and trial attorney, burst into tears during the hearing and they kept flowing for hours afterward.
"I’m sad. What can I tell you?" she later told PEOPLE, sounding drained and defeated, on her way back to her Valencia, California home with her daughter, Bailey Donorovich, 21.
"I have no tears left," she says.
Compassion & Choices, which filed the lawsuit on behalf of O'Donnell and other plaintiffs, immediately vowed to appeal.
"We respectfully disagree with the court's ruling," John Kappos, a Newport Beach, California-based partner for O'Melveny & Myers who is handling the case for Compassion & Choices, said in a news release.
"We are hopeful an appeals court will recognize the rights of terminally ill adults like Christy O'Donnell," he said, "who are facing horrific suffering at the end of their lives that no medication can alleviate, to have the option of medical aid in dying."
A spokesman for Californians Against Assisted Suicide, which opposes the lawsuit, said the group would not comment until after the judge issues his written decision.
Though the appeal will likely get an expedited schedule O'Donnell, who has Stage IV lung cancer that has spread to her brain, spine and left rib, is worried she may not live long enough to see it through.
"It's clearly not the end," she said. "It just might be the end for me."
Though O'Donnell said she and Bailey were "emotionally and physically exhausted" from the day's events, she vowed to keep fighting to die her way – instead of the protracted, painful way that's been described to her by doctors – even as she continues to fight to live.
Doctors have told O'Donnell she will likely die drowning in her own fluids. She is morphine-intolerant.
"It's been a tough day but I have not given up," she says. "I'm not going to give up but it's certainly not the 47th birthday I would have hoped for."
The last chemotherapy regimen O'Donnell was on was causing neuropathy in her feet and swelling in her legs so her doctor took her off it.
On Tuesday she will start on a lower dose of the first chemo regimen she was on – the one that had her puking her guts out for days on end but which her doctor hoped he could remedy by lower doses.
"We'll see if my body will react the same way as last time which was very badly," she says. "He's doing what doctors do – exhaust every possible avenue to continue to live."
Courtesy Christy O'Donnell