RAPID CITY, S.D. -- A western South Dakota high school won't allow a student who has brain cancer to walk during its graduation ceremony because she is a few credits short of being able to graduate.

Meredith Erck, 17, wasn't sure whether she would live to see graduation day, The Rapid City Journal reported.

The Central High School student had colon cancer before she was diagnosed with brain cancer in 2015. Between surgeries and recovery, she couldn't complete all of her classes on time.

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Meredith hoped she could walk the stage with her friends and her twin brother this weekend, and formally receive her diploma at a later date. She is six credits short, but expects to finish half over the summer and the remaining before the end of the next academic year.

But Rapid City school district officials said in a statement that her participation without credit completion would be unfair to other students who met the criteria to graduate.

"If we grant one exception, we have opened the door to any and all future requests. High school administrators believe that allowing exceptions diminishes the accomplishments of the graduates," the statement read.

Meredith's mother, Laura Polanco, disagreed.

"She just wanted to participate in graduation with the kids she's been in school with since kindergarten," Polanco said. "She knows she's not finished, she knows she's not getting a diploma."

Polanco said Meredith did her best to keep up with schoolwork while staying in the hospital for chemotherapy and radiation treatments.

In a letter to the school's principal, family friend Bethany Wojahn pleaded: "This was not a failing on her part. This was unfair. This was rare. This was life-changing. I see no possible purpose that can be served by disallowing her to walk with her brother on graduation day, even if only to hold his hand while he receives his diploma."

Principal Michael Talley declined to comment directly to the newspaper.

Meredith's mother said there is a 30 percent change the cancer will return, and it will take her daughter five years to fully recover from her illness.

Meredith is expected to finish her remaining credits before the end of the next academic year.