"Her words were, 'Yeah, just let me know when you need me.'" her dad Brian told ABC News.
Her twin, Bradley, was diagnosed with acute myeloid leukemia, an aggressive form of cancer, in the fall of 2014. Charlie, they discovered, was the perfect match to donate cells needed to help save her brother's life.
"For us to be fortunate enough for Bradley to have a twin sister who's a perfect match; we were speechless. Not everyone is so lucky," he said.
In January, Charlie's parents asked her if she would be willing to undergo the procedure, and she said yes.
"She didn't understand the whole medical process, but what she did understand was she wanted to help her brother," Godish said. "What Charlie did for her brother and my wife and I was nothing short of amazing."
Godish said his daughter didn't complain once and even wore her bandage for longer than needed to show how proud she was to help. Bradley's doctor, Dr. Jennifer Schneiderman, said it is not unusual to look to close family members to donate in high-risk situations like Bradley's.
"She [Charlie] doesn't feel it at the time, but typically patients will feel some soreness for 36 to 48 hours and then they're fine," she said.
Godish said that he hopes both his children keep the lesson of Charlie's selflessness with them for years to come.
"We really hope as parents they learn from this -- to always be selfless to always help somebody out, to always give," he added. "This shows how valuable love and life is and I hope they never take life for granted."
The family is sharing their story now because Bradley is in remission. The pair just started kindergarten.