"He said, 'You're having migraines,' " Debbie Ziegler, Maynard's mother, told PEOPLE in an interview Oct. 11, "and sent her home" – without doing an MRI.
That initial reaction by her doctor – while heartbreaking – is not that uncommon with brain tumors, experts say.
"A young woman with migraine syndrome, you wouldn't think about a malignant brain tumor," Sean Grady, chairman of the neurosurgery department at the Hospital of the University of Pennsylvania in Philadelphia, tells PEOPLE.
Elizabeth Wilson, CEO of the American Brain Tumor Association, agrees.
"What she experienced is probably common," she tells PEOPLE. "It sounds to me like she was having general symptoms. What often happens is it isn't until one or all of those things come on really powerful or you have a seizure that gets you to the ER and the diagnosis."
As millions of people now know, Maynard, 29, had terminal brain cancer and became the face of the controversial right-to-die movement during the last weeks of her life.
She ended her own life Nov. 1 by taking medication prescribed to her by a doctor – something that is legal for certain terminally ill patients in Oregon, where she, her husband Dan Diaz, her stepfather Gary Holmes and Ziegler moved so she could get access to the state's Death with Dignity Act.
On Oct. 6, she launched an online video campaign with Compassion & Choices, an end-of-life choice advocacy organization, to fight for nationwide access to the law.
Courtesy Brittany Maynard
A Deadly DiagnosisMaynard and Diaz, 43, were away in California's wine country last New Year's Eve when she fell ill.
"Dan called me while they were on their way to the hospital," said Ziegler, 56. "When I flew up there … the first thing I saw was the nurse holding her up and screaming her name over and over again, so I thought she was dead.
"It was so scary," she continued, crying at the memory.
The following day, Maynard was diagnosed with a malignant brain tumor.
After a partial craniotomy and partial resection of her temporal lobe to stop the growth of the tumor, it came back bigger and more aggressive than ever two months later. This time, doctors said it was likely a Grade 4 glioblastoma and told her she had at most six months to live.
Without opening up her brain to take a sample of the tumor, they couldn't be sure, though, they told her – one of many frustratingly inexact answers she got during her illness.
"It's a disease that needs more research and needs to be better understood," she told PEOPLE Oct. 9. "And in the meantime, my mom's sitting next to me saying it should be funded better."
The lack of knowledge about her illness added yet another layer of fear.
"As a sick person all you want to do is to be able to walk into a doctor's office and get the answers," she says, "and be able to look at the physician and feel they know what they're talking about and have them fix you up. That has not been my experience."
"That's always been my experience as a really healthy person, so it's been a scarier experience having a type of cancer that's not well understood in the grand scheme of things," she added. "For me, not being able to cured has been terrifying."
Maynard's tumor seemed to mystify doctors, she told PEOPLE.
At one point, they told her they thought it could have been growing very slowly for as long as 10 years, she said.
"The doctors are shocked at how large my tumor is," she said. "They said they've never seen one this large. It's in the parts of my brain that control speech and language, so they think those functions have shifted elsewhere in my brain since I can still speak."
Experts agree there is still a lot unknown about many brain tumors and more funding is needed for research.
"It could happen to any of us," Wilson says. "We just don't know who or when or why. That's what our research funding goes toward."
Sean Grady says patient diagnosed with glioblastoma often face a very grim prognosis.
"The odds are definitely against you for long-term survival," he says. "Radiation and straightforward chemotherapy can improve things by a series of months but not by a series of years."
For Maynard, though, the horrific side effects she faced from radiation, which would have had to encompass nearly her entire brain, and chemotherapy were not something she was willing to endure.
Hope DwindlesAfter her initial diagnosis in January, Maynard began to research death with dignity.
She and Diaz even watched How to Die in Oregon, a documentary that chronicles the decision of Cody Curtis, a 54-year-old mother of two, to end her own life rather than die of liver cancer.
"You can see it happen," Diaz told PEOPLE last month. "You can see her die."
Even after announcing she intended to end her life Nov. 1, Maynard continued to hope for a miracle.
"My mind is not closed to the option of a cure," she told PEOPLE on Oct. 9, "so if there are physicians who think they can help, I very much want to hear from them."
Maynard has said she and Diaz were trying to have a baby when she fell ill, so many people asked if she thought about freezing her eggs so he still could – and so her mother would have a grandchild.
"I'm just not able to do that because I was so looking forward to being a mother," she told PEOPLE. "And honestly if there's one thing that can continue to bring me to tears it's that – how much my husband and I wanted children."
Plus, "I can't bring myself to have a child and die and leave my child motherless so young," she said. "I know that happens but I can't bring myself to have a baby and know I wouldn't be there for that child."
Courtesy Brittany Maynard