Daughter Helps Care for Siblings as Mom Fights Rare Cancer

— -- After raising nine children, including three sets of twins, Catherine Kelly, 41, didn't initially worry when her knee started to give out last November.

Kelly's sister-in-law Carolyn Barbour-Wilson told ABC News that Kelly was upbeat until her doctor's appointment.

The doctor told Kelly that she had a rare form of cancer called osteosarcoma, where the tumor appears in the bone. Barbour-Wilson said that the stage 3 tumor had so significantly damaged Kelly's knee that doctors decided they needed to entirely replace it.

Before she could have surgery Kelly, who lives in Bothell, Wash., had to have chemotherapy, leaving the busy mom barely able to move.

"It's taken me almost completely out," Kelly told ABC News affiliate KOMO-TV. "I'm nauseous. I used to cook, clean, you know walk a million steps around this house taking care of all the children."

Barbour-Wilson said she, along with Kelly's older twin daughter, age 25, have been pitching in and coordinating meal delivery and childcare to help Kelly and her husband raise their seven other children, who range in age from 2 to 18.

"It’s a challenge getting them bathed and changed and [do] laundry," Barbour-Wilson said of the large family. "There’s no one there to do it."

This summer doctors were able to remove the tumor by completely replacing Kelly's knee with a prosthetic. An infection a few weeks later necessitated a second knee replacement that left Kelly completely bedridden.

"The hardest thing for Catherine is not being able to be there for her children," Barbour-Wilson said.

Currently Kelly is back in the hospital for another round of chemotherapy, but she told KOMO-TV that she hopes she'll be back to feeling more normal by Christmas.

"I can get back to doing what I'm used to doing, which is taking care of all the kids and keeping them happy and loved," Kelly said. "I'm fighting it with everything I have, and I'm moving forward and I'm going to kick this thing and get back to life."