But the worst was yet to come.
"The next day, she woke up and she couldn't open her right eye all the way," Beitz said. "Her eyelid wouldn't go all the way up. That was scary. We knew that wasn't a good sign."
On Jan. 6, Erin had an MRI, which revealed a tumor on the base of her skull. She was admitted to SUNY Upstate that day.
When her local doctors were stumped as to how to proceed given her unusual symptoms and the location of the tumor, Erin's parents took her to The Children's Hospital in Boston.
"They looked at her scans and they did some of their own scans," Beitz said. "They started discussing options with us."
Because of the location of the tumor, a less-invasive needle biopsy, in which cells are extracted from a growth with a needle, was not possible. Erin had to have a full craniotomy, cutting open her skull to access the tumor.
Two weeks later, doctors gave the family a diagnosis: lymphoma.
"They weren't expecting that," Beitz said. "Nothing added up -- her symptoms, the blood tests. It was very strange."
Unfortunately, Erin's cancer isn't like other cancers.
"It's lymphoma, which means it's a cancer of the blood," Beitz said. "So it's in her blood cells. It's not like, say, breast cancer, where it's in the breast cells, and if you remove that tumor, you're more likely to have removed all the cancer. It's throughout her body."
There's also the location of the malignant tumor: right at the base of Erin's skull.
"It's impacting the nerves in her brain, which is how she even developed any symptoms," Beitz said. "There's no possibility of surgical removal."
Fortunately, the doctors have told the Beitz family that Erin's prognosis is good. She will have to undergo rigorous chemotherapy for the next six to eight months, spending four to five days in the hospital for each treatment, then getting 10 to 12 days of rest between treatments.