Update for those who are interested:
The cancer is on the brain stem, which usually results in a poor prognosis (chance of recovery). However, my brother and sis-in-law are meeting with the doctors today and will be discussing the idea that the cancer isn't as serious as something that requires absolute, immediate chemotherapy/radiation.
Hopefully, Seanna won't have to go through radiation, since it stunts growth and development when done in young children.
Thanks for your support, everybody!